Flash flooding triggered by a strong thunderstorm killed at least eight people in southern Utah, authorities said. Five others remained missing early Tuesday.
"This hit with a vengeance we haven't seen for some time," said Kevin Barlow, the assistant fire chief in Hildale, a town on the Utah-Arizona border. Several children and mothers were among the dead or missing, he added.
Barlow said that an SUV and a van carrying a total of 16 people had been swept away by the flooding. They were "hit by a large wall of water and debris," Washington County Emergency Services said in a statement.
The women and children were thought to be coming back from a park in the area when the flash flood hit, according to Barlow.
Three people were rescued during the ordeal, which occurred around 4:40 p.m. local time (6:40 p.m. ET).
The floods came after heavy rains fell in the canyons just north of Hildale and its sister town of Colorado City, Arizona, sending waves of water barreling through the streets. They sit at the foot of picturesque red rock cliffs about 315 miles south of Salt Lake City.
Hildale resident Guy Timpson told NBC News that at least 300 people were trying to sort through "a mass of debris."
"We've got quite an effort going on," he said. "It's been pretty amazing to see the community coming together to do what they can."
He added that excavators and heavy lifting equipment were on the scene.
Ted Barlow, who lives in Colorado City, described the storm as among the worst in decades.
The downpour lasted for about 20 to 30 minutes and brought rapid and intense flooding from nearby mountains.
"Everyone is family here, and it's a tragedy however you look at it," Barlow said.
Search and rescue teams were scheduled to resume efforts to find the missing people at daybreak.
The National Weather Service had issued a flash flood warning earlier in the day, leading nearby Zion National Park to close all slot canyons as a precaution.
More thunderstorms are predicted for Tuesday with up to half-an-inch of rainfall predicted, according to Weather Channel senior forecaster Kevin Roth.
"If that hits all at once it could be bad," he said. "But even if it doesn't hit them directly and ends up in the mountains they could still be affected."
Hildale served as a home base for polygamous sect leader Warren Jeffs.
Members of the sect, whose members believe polygamy brings exaltation in heaven, are believed to be discouraged from watching TV, using the Internet or having much contact with the outside world.
More than four years after Jeffs was sentenced to life in prison for sexually assaulting underage girls he considered brides, the community is split between loyalists who still believe Jeffs is a victim of religious persecution and defectors who are embracing government efforts to pull the town into modern society.
The community is a patchwork of upscale, elegant residences surrounded by large walls and unfinished, dilapidated houses that remain just as they were in the early 2000s, when Jeffs ordered that all construction stop in Utah to focus on building his compound in Texas.
Henry Austin and the Associated Press contributed. This article originally appeared on NBCNews.com.