"We do have whole streets that have maybe one or two houses left on them, and the rest are just slabs," said Kharley Smith, emergency management coordinator in Hays County, Texas.
Crews are still surveying damage, she told reporters Sunday; between 350 and 400 homes in the Texas county are gone, and more than 1,000 were damaged. Two main bridges washed away, she said, and others sustained major structural damage.
In San Marcos, Texas, a city between San Antonio and Austin that was among the hardest hit areas, Fire Marshal Ken Bell said at least one person was confirmed dead. Crews are searching for three missing people, he said, and others are trapped in areas that authorities can't reach because bad weather has forced them to stop air rescues.
It was not immediately clear whether the fatality was one of the people reported missing. Authorities don't yet know how devastating the damage is, and they're bracing for the possibility that more rainfall could send floodwaters surging back into the city, he said.
Forecasters warned that new thunderstorms pushing through the area Monday could cause heavy rains. And with the ground already saturated, even just a small amount of rain could still have devastating consequences, they said.
"Only an inch or two of rainfall could quickly lead to more flash flooding concerns," the National Weather Service said in an advisory
"Right now is not the time to return to your homes," Bell said Sunday after the severe weather forced the evacuation of hundreds of residents.
"We have infrastructure damage throughout the entire county (of Hays)" he said. "There are power lines down, debris in the roadways, bridges undermined -- this is not the time to start moving."
It was a warning other authorities in the region echoed after rainfall broke records and river banks in northern Texas and Oklahoma overnight.
At least two people died in storms that hit Oklahoma. On Saturday, a 33-year-old woman in Tulsa died after her car hydroplaned, said Keli Cain, the state's emergency management spokeswoman.
Nearby in the town of Claremore, a firefighter died when he got swept into a storm drain while attempting a high-water rescue Sunday morning as emergency crews scrambled to pull residents from floodwaters, CNN affiliate KTUL reported
With more rain falling, the torrents have already pushed Oklahoma City handily past a rain record, and rescuers have carried out at least 48 high-water rescues.
More than 1,000 in shelters
For hours, Hannah Pullen made desperate calls to her father, who was stranded in his truck on a flooded highway just outside San Marcos.
Danny Pullen, 68, said he wasn't sure if he'd survive. He told her he loved her.
His daughter pleaded with him not to give up hope. "Just hold on," she told him. "Please don't leave."
Hours later, a helicopter came to the rescue, CNN affiliate KEYE reported
, hoisting him from the top of his truck to safety in a dramatic air rescue.
Others in the area were plucked off rooftops by rescuers until worsening weather stopped the helicopters from circling.
In Hays County, hundreds of people were rescued or evacuated from their homes, according to sheriff's office spokeswoman Lt. Jeri Skrocki. National Guard troops arrived early Sunday to help with evacuations and flood control.
More than 1,000 people were in shelters Sunday afternoon, Smith said.
Emergency management officials are not just urging everyone to stay inside, they're making it mandatory. Officials from Hays County and the cities of San Marcos and Wimberley issued a curfew from 9 p.m. Sunday to 7 a.m. Monday because of the potential safety concerns posed by the flooding.
"Turn around, don't drown" said Hays County Judge Bert Cobb, who's presiding over the county's emergency management operations. "If you go around a water barrier, there may not be anybody to come help you ... so just don't do that," he pleaded. "If you think you can make it -- think twice. " he said.
The Pedernales Electric Cooperative, whose crews were working to restore power in the area, shared photos on social media of devastating damage, saying conditions were making accessing equipment difficult. Some of the power cooperative's facilities had been washed away, officials said.
Houston-area dam a concern
Nearly 200 miles northeast of Hays County, near Houston, an area of about 400 homes around Louis Creek Dam is under mandatory evacuation, according to Miranda Haas with the Montgomery County, Texas, Office of Emergency Management. The dam has not breached and workers continue to pack soil on it.
"Our construction efforts have been phenomenal, they have made tremendous progress, it's just the weather is not letting up at all," she said.
Another 2 to 3 inches of rain could soak the evacuation area and bring damaging winds through Sunday evening, according to the latest forecasts
from the National Weather Service. And, there's more to come. An additional 2 to 4 inches are possible Monday as rains continue.
Wichita Falls 'historic flood'
Wichita Falls, Texas, was warned that its river could widely overflow its banks and severely flood broad swaths of surrounding areas, as well as large parts of the city. Officials published a potential flooding map with a red zone nearly the size of the city.
"Predictions from the National Weather Service indicate that significant flooding along the Wichita River is very likely," the town's emergency management agency said. "The National Weather Service is calling this an 'historic' flood event."
The agency called for the voluntary evacuation of 2,177 homes.
Olivia McKinney had tears in her eyes as she crammed items into the trunk of her car Saturday.
"I really don't want to leave my home," she told CNN affiliate KAUZ
. "I don't want to leave it. ... I'll be glad when it's over."
Wichita Falls is having the rainiest May ever recorded there and "could set an all-time record for rainiest month ever recorded there," said CNN' weather producer Sean Morris.
Broad, muddied flood waters gushed across fields, towns and roads in images from both states, turning land expanses into lakes, half burying cars and houses.
Blue and red emergency vehicle lights bounced off dark, watery surfaces, as rescuers worked through the night.
On the National Weather Service map, chartreuse squiggles signified overflowing rivers and creeks from southern Texas to northern Missouri. Much of the state of Oklahoma was covered in the bright green.
Motorists abandoned cars in streets and parking lots, as rising waters took them over. The weather service put out its usual flood mantra to drivers, "Turn around, don't drown" when encountering flooded roads. "Most flood deaths occur in vehicles."
The weather service also told campers and hikers to seek higher ground.
In addition to the worst-hit areas, flood watches and warnings reached from the Texas and western Louisiana Gulf coasts up through eastern Kansas and western Missouri.
In middle of drought
Despite the heavy rain, western Oklahoma and parts of the Texas Panhandle and central Texas are still facing moderate drought or abnormally dry conditions, according to the U.S. Drought Monitor. The rainfall should put a dent in it, though.
But the current deluge might be a bit much.
"I didn't hesitate telling people... there's going to come a day when we're gonna wish the rain would stop," Wichita Falls Mayor Glenn Barham told CNN affiliate KAUZ. "I think that day is probably here."
In 2011, drought and wildfire brought heavy damage to Texas.
The drought caused at least $5 billion in economic damage, and wildfire damage amounted to tens of millions of dollars, authorities said.