The flash flood "hit with a vengeance," Assistant Fire Chief Kevin Barlow said

Eight people died and five more were still missing after a flash flood triggered by a powerful thunderstorm swept through the polygamous community of Hildale, Utah, on Monday night. The town was once home to polygamist sect leader Warren Jeffs.

Sixteen people riding in a van and an SUV were hit by a wall of water and debris, says Michelle Chatwin, an employee for Hildale City, while on they were on their way home from a local park at about 5 p.m MST.

“They had apparently stopped to watch the flooding from their cars when more flood waters came from behind and swept them away,” Chatwin tells PEOPLE. “This is the heaviest rain we’ve seen here in this area in a very long time.”

The downpour lasted about 30 minutes and brought quick and intense flooding from the mountains nearby.

“This hit with a vengeance we haven’t seen for some time,” Assistant Fire Chief Kevin Barlow told the Associated Press.

The flood “obviously caught these people off guard,” Barlow added. “Witnesses say they were backing out of it trying to get away from it and it still swept them in.”

The National Weather Service had issued a flood warning earlier on Monday, resulting in nearby Zion National Park closing all slot canyons as a precaution. Barlow didn’t know if residents were aware of the warning.

More thunderstorms are predicted for Tuesday as search efforts continue.

“We’re pretty used to flash flooding, but this is significantly more than what we’re used to,” Barlow told the AP.

It’s unclear if those caught in the storm had any tie to Jeffs’ sect. Most of the people who live in the community are members of the Fundamentalist Church of Jesus Christ of Latter-day Saints.

Members of Jeffs’ sect believe polygamy brings exaltation in heaven, and it’s believed they’re discouraged from watching TV, using the Internet or having much contact with the outside world.

Jeffs was convicted of sexual abuse of a child and aggravated sexual abuse of a child and sentenced to life in prison after a trial that became a strange spectacle in which Jeffs represented himself and said nothing during most of his summation.

Reporting by CATHY FREE