Hong Kong (CNN) -- They stepped onto the evening ferries in Hong Kong's crowded harbor to watch the sky light up with fireworks to celebrate China's National Day. Instead, the night ended in chaos and tragedy.
Two ferries collided Monday night, upending one of the vessels and sending passengers into the water. At least 38 people died. Rescuers picked up 123 survivors and are still searching for a countless number of others who are missing.
Passengers on board the ferries said they had only moments to escape.
"First it was up to here and then here. The water rose so quickly," one woman, who declined to be named, told CNN affiliate i-Cable. "We thought we were going to die for sure."
The boat rolled violently before it partially sank.
"I opened the window and pushed a child out. I put a life jacket on him and pushed him out first," he told i-Cable. "At the time, it was very chaotic. The boat was completely standing straight up in the water. It was chaotic. All the tables and chairs were everywhere. It was like a slide; everything was sliding down."
Authorities are investigating what caused the crash, Hong Kong's most lethal maritime accident in more than 40 years. Police have arrested seven crew members from the vessels on suspicion of endangering passengers.
The collision involved a passenger ferry traveling from Hong Kong Island to Lamma Island and a vessel owned by the Hong Kong Electric Company, which was carrying company employees and their families to watch the scheduled fireworks display. Government officials said it occurred off Lamma's coast about 8:20 p.m.
"I thought we'd hit a rock or a lighthouse," said Chris Head, a teacher who was on the passenger ferry. He said the vessel went from what felt like full speed to "an abrupt halt."
Head said the force of the impact threw him out of his seat at the back of the ferry, which was not very full of people.
As the damaged ferry began to move toward a pier in the small town of Yung Shue Wan on Lamma, Head said, he could see the other boat had started to sink into the water vertically, like the Titanic.
"It was very dark," he said. "There were very few lights on board."
According to the Hong Kong Fire Services Department, which led the rescue, the vessel began to sink quickly after the impact. It said low visibility and many obstacles on board made work difficult for rescuers.
"After 10 minutes out, a boat crashed into ours from the side at very high speed," one male survivor from the accident told the South China Morning Post, a local newspaper. "The rear of the ferry started to sink. I suddenly found myself deep under the sea. I swam hard and tried to grab a life buoy. I don't know where my two kids are."
Residents on Lamma, a lightly populated island southwest of Hong Kong Island, reported being awakened in the middle of the night by the massive rescue operation going on offshore.
On Tuesday, the front of the stricken vessel was still sticking out of the water, tethered to a barge equipped with a crane just a few hundred meters from the coast of Lamma. Emergency services boats surrounded the scene, and divers conducted a search.
Despite a hole torn in its bow, the passenger ferry was able to dock safely after the crash. Government officials have not confirmed whether passengers aboard that vessel were injured, but Head said nobody around him appeared to have been hurt.
The narrow sea lanes leading into Hong Kong's main deepwater harbor are some of the busiest in Asia, with giant commercial freighters, ocean liners, passenger ferries and private boats of all sizes sharing the waters.
Hong Kong is home to more than 200 outlying Islands, including Lamma. Hong Kong Island is on the south side of Victoria harbor, with Kowloon forming its northern shore. North of Kowloon lie the New Territories, which stretch all the way to mainland China.
Monday's crash is Hong Kong's most lethal maritime accident since 1971, when 88 people died after the ferry Fat Shan capsized between Hong Kong and Macau amid a typhoon.
CNN's Paul Armstrong, Jethro Mullen, Judy Kwon, Pamela Boykoff and Mark Morgenstein contributed to this report.