(CNN) -- One woman died and authorities are searching for the body of another -- swept away as she sat on a car, face-to-face with firefighters -- due to raging floodwaters in San Antonio, which braced for yet more drenching rains Saturday night.
At one point Saturday, a storm and subsequent floods had knocked out power to about 12,000 customers and spurred the closure of dozens of streets in San Antonio and the surrounding county, authorities said.
Scores of people had to be evacuated due to floods and other issues, and Fire Chief Charles Hood noted there had been about 250 water-related calls -- in addition to ones for things like medical emergencies, accidents and more -- in the first 15 hours of Saturday.
The greatest concern had to do with people getting too close to fast-moving, deceptive and unpredictable floodwaters.
"We're asking folks to observe low-water crossing (warnings), to use common sense and to stay off the road if possible," Mayor Julian Castro said.
The confirmed fatality -- a woman around age 30 -- was reported around 7:30 a.m. (8:30 a.m. ET), and her body was about three hours later, police Chief William McManus said.
Some time later, a female driver, about 60 years old, went into water that was 4 feet above flood markers. Firefighters got to her vehicle and broke a window -- with one firefighter cutting his hand -- Hood explained. Then, as the would-be rescuers tried to get her from on top of her vehicle, "the currents changed and washed that vehicle away," the fire chief said.
Hood characterized authorities' efforts now to find this woman as "a body recovery." By Saturday afternoon, she still hadn't been found.
"You can imagine how emotionally spent you are to try to rescue somebody, you're face-to-face with them, and then they're washed away," Hood said of his distraught firefighters.
The chief warned more people may be missing and perhaps dead. Firefighters happened to spot this woman going into the water before they rushed to rescue her; there may be others, Hood pointed out, that firefighters or others don't see get trapped in floodwaters.
"Turn around and don't drown," multiple officials repeated at a Saturday news conference.
The problems began with torrential rains late Friday that continued into Saturday, triggering flash-flood warnings across South Texas.
San Antonio International Airport received 9.57 inches of rain Saturday morning alone, CNN meteorologists said.
The city's Leon Creek was at 27.1 feet at 2:16 p.m. Saturday -- well above the flood stage of 15 feet.
"Disastrous flooding puts near 7 feet of flow in buildings in the jet engine test facility at Kelly AFB," the National Weather Service said. "Secondary and primary roads and bridges are severely flooded and dangerous to motorists above Highway 90 to below (Interstate 35)"
Flood warnings have also been issued for the San Antonio River, Medina River and Salado Creek, all of which are above flood stage.
In an interview with CNN affiliate KENS, San Antonio resident Mary Alice Galicia described how water enveloped her house.
"It was underwater 20 minutes ago," she said. "I came over here. I own the property, and my daughter said that she couldn't get to her car. Her car's all flooded. The property -- the water's all swarming through the whole house. I just came over to check to see what I could do, but there's nothing that I can do right now."
Galicia doesn't have flood insurance because she "never imagined this would happen," she said.
"But it's not stopping. I thought it was gonna stop," she said about the water damage.
San Antonio's previous record flooding in 1998 was devastating, caused by heavy rains throughout south Texas and by a plume of moist air from Hurricane Madeline off the Mexican west coast. A total of 11 people died in San Antonio that weekend, with property damage estimates at $750 million, a city report said.
In all, the south Texas flooding killed 31 people during that October 1998 weekend: 26 drownings, two tornado deaths, two heart attacks and one electrocution-drowning, a federal report said. At least 17 of the drowning victims were in vehicles driving into the water or swept away by rising water, the U.S. Commerce Department report said.
CNN's Michael Martinez and Tom Watkins contributed to this report.