Aid workers in the capital of Port Vila described homes and shops flattened, swaths of trees plowed over and residents seeking shelter in schools and churches -- or with neighbors.
At least six people are dead, but communication with many of the 80-plus islands in the archipelago is impossible, so the fear is that toll will climb. The deaths reported by the National Disaster Management Office are just from Port Vila.
It is unclear how many thousands will be displaced by the massive storm that bore the might of a Category 5 hurricane when it pounded the islands for most of a 24-hour period.
"It's like a bomb has gone through," said journalist Michael McLennan, who lives in Port Vila. "It's really quite apocalyptic."
Most buildings were destroyed or damaged, he told CNN on Sunday morning. Many roads are blocked by fallen trees or power lines.
Hardly a tree stood straight after Pam bellowed across the South Pacific nation, where some 260,000 people live, many in flimsy homes built of thatch.
Cleanup efforts are underway, according to Colin Collet van Rooyen, Oxfam country director in Vanuatu.
It appears Bauerfield International Airport will reopen Sunday afternoon for emergency flights. An Australian C-130 took off for Port Vila with emergency personnel from the defense department. The Australian air force will send two cargo planes loaded with relief supplies, the government in Canberra announced.
The main objective now is to get disaster response teams into Vanuatu and kick-start the humanitarian operation, Sune Gudnitz, regional head for U.N. aid agency OCHA, told CNN from Fiji, about 600 miles away.
His agency has had word of much destruction on Efate, the island that houses the capital, where the violent winds around Pam's eye roared through, and from the southern island of Tanna, he said.
Only a little information has so far trickled out from beyond the capital, but Gudnitz, said that he fears the worst.
"Unfortunately, the more that comes out, the worse it looks," said Gudnitz. "I should say it's really a case of the worst-case scenario for the country and for the people."
Vanuatu President Baldwin Lonsdale, who was at a U.N. conference on disaster reduction in Japan on Saturday, appealed for help for his shattered nation.
"I am speaking with you today with a heart that is so heavy. I do not really know what impact Cyclone Pam had left on Vanuatu, as there are no confirmed reports as yet," he said.
"I stand to appeal on the behalf of the government and people of Vanuatu to the global community to give a lending hand in responding this very current calamities that have struck us."
Pam was the equivalent of a Category 5 hurricane before notching down to Category 4 after landfall at 11:23 p.m. Friday local time. CNN's weather center said 155 mph (250 kph) winds blasted the island nation, with gusts up to 200 mph (325 kph).
By overnight Saturday, the damage was done. CNN meteorologist Ivan Cabrera noted that, by then, Pam had passed all the nation's islands and was moving over open water.
As it moved over cooler ocean waters away from Vanuatu, the storm further weakened Sunday. It had sustained winds of 132 mph (213 kph), said the Joint Typhoon Warning Center in Pearl Harbor, Hawaii.
The damage it left behind is "unbelievable," according to the Australian Red Cross.
"Humanitarian needs will be enormous," the aid agency tweeted. "Many people have lost their homes. Shelter, food and water (are) urgent priorities. "A UNICEF Australia post, meanwhile, spoke of "countless homes torn apart, communities in ruin."
But the airport in Port Vila has been damaged and it's not clear when it will be able to reopen to allow relief flights to land. The U.N. aid agency hopes to get its first team on the ground with vital aid on Sunday, Gudnitz said.
Vanuatu's remote location won't help the international response. Port Vila is more than 1,100 miles northeast of Brisbane on Australia's east coast, and some 1,375 miles north of Auckland, the closest city in New Zealand.
Until international teams can get in, it will be up to humanitarian agency staffers on the ground and the local communities themselves to do what they can among the wreckage.
Many people will be spending another night in emergency shelters.
Trees piled high
At least they won't have to face the horrors of the height of the storm.
At that point, Alice Clements was cowering under a bathroom sink. "But all what I could think about during that time is the people who might be literally clinging to coconut trees for their lives, and trying to hold on in those horrific winds," the UNICEF spokeswoman said.
There's no power in the whole of Vanuatu, Clements said, making it impossible for people to recharge their cell phones to call in. The water supply is also cut off, adding to people's difficulties.
Another UNICEF staffer in Port Vila, Andrew Parker, told CNN that he'd been through many cyclones, but this one "just went on and on forever."
The winds and rain only started to subside about 1 or 2 p.m. on Saturday, he said, having raged since 5 p.m. on Friday. Port Vila alone ended up with about 9 inches (230 mm) of rain in a 36-hour period, which is 70% of its rainfall for the month.
Only one cell phone tower was still standing in the whole of the archipelago, in Port Vila, according to Parker.
Vanuatu has officially declared a state of emergency due to devastation caused by Pam, opening the door for other countries -- like Britain, which is already offering almost $3 million -- to help.
"Port Vila looks like an absolute bomb has hit it," World Vision emergency specialist Chloe Morrison said.
Trees blocked the path of Morrison's vehicle as she drove around the capital. "They've fallen across in piles so high in some places you can barely see over the top," she said.
Strongest since Haiyan
Pam is the South Pacific's second strongest cyclone since record-keeping began in 1970. And it's the strongest of any type since Super Typhoon Haiyan smashed the Philippines in 2013, obliterating parts of Leyte.
Vanuatu, which lies east of Australia, is an archipelago comprising 83 small islands, about 65 of them inhabited and many remote and lacking infrastructure. People away from the capital live much like their ancestors did generations ago.
Homes are built of weaker materials, including straw and corrugated steel, and may have had little stamina against Pam's raging winds.
"This is often a tropical paradise island and a lot of these houses are what you would expect on an island. They are thatched roofs and thatched walls, and just not able to withstand a Category 5," Morrison said.
"We've seen villages literally blown away."
Villages 'literally blown away'
Pam "left no island untouched," Morrison added. "And the devastation that will be on those smaller, remote islands -- I can't even imagine it."
"Once we start looking further afield from Port Vila, we are going to see more destruction because the houses there would be in a much different condition from what we have in Port Vila," Gudnitz said.
"It's a disaster, there's no other way to describe it, really."
The Adventist Development and Relief Agency, the humanitarian arm of the Seventh-day Adventist Church, said it was still waiting to hear from all its team in Vanuatu. Five have not been accounted for on Pentecost Island and five on Malakula Island, presumably unable to communicate because cellular networks are down, the organization said.
Field staff have reported that even families whose homes had survived two previous cyclones lost them during Pam.
"Families are trying to gather as much as they can," said Mark LeRoux, the organization's Vanuatu country director. "Even sturdy houses didn't make it -- walls and roofs came down."
Hunkered down, terrified
Even in a concrete house in Port Vila, emergency worker Morrison was terrified by the whirring force. She huddled in a back room with seven other people.
"Seven hours hunkered down and it's still not safe to go outside," she said early Saturday. "The winds are still really howling." It sounded like there was an angry ocean at their door.
As a piece of tin twisted off the roof and landed by a window, Morrison felt lucky to be shielded by solid walls.
One positive amid the devastation is that Vanuatu has known that Pam was coming for more than a week, giving time for people to evacuate to shelters, though not every island even has a concrete structure, Morrison said.
The biggest priority now for many will be access to clean water, she said. In some outlying communities this was difficult even before Pam hit.
There is also the issue of food. Many people on Vanuatu's islands are subsistence farmers and the cyclone may have destroyed most or all of the crops they rely on to survive. McLennan, the journalist who lives in Port Vila, said crops with roots fared much better through the storm than those that grow on trees.
World Vision's staff hopes preparations will have paid off. They had positioned clean water, food, blankets, tarpaulins, and shelter, hygiene and kitchen kits in key places before the cyclone arrived.
Next cyclone brewing
Pam isn't done yet, heading south-southeast at a 32 mph (52 kph) clip, the Meteorological Service of New Zealand
reported at 7 a.m. Sunday.
It should start affecting New Zealand's North Island late Sunday, though the good news -- according to CNN's Cabrera -- is that it won't be the same "monster storm."
The weather service said, "Heavy rain and strong wind warnings and watches are in force for the northern and eastern parts of the North Island from this evening through to Tuesday. "
New Zealand's official weather agency forecasts up to 8 inches of rain and 100 mph wind gusts in parts of that island, though the overall impact won't be anywhere near as bad as in Vanuatu.
In the meantime, a new cyclone -- Nathan -- is brewing over Queensland, Australia. It is expected to reach Vanuatu this week.