At least 16 people have been killed in flash floods in the US state of Utah with four others missing as of Tuesday night.
Four people died in flash floods in Zion National Park, and three were missing after the group went to explore a small, narrow canyon, shortly before heavy rains began, officials said on Tuesday.
In a statement, park officials said the group's vehicle was found at a trailhead on Monday evening in the Keyhole Canyon area, and that a search began on Tuesday morning.
"Of the seven individuals involved, three fatalities are confirmed and the remaining four are missing," park spokeswoman Aly Baltrus said in a statement. Baltrus confirmed the fourth death later on Tuesday.
Park officials said the group of four men and three women set out on Monday before park officials closed the canyons that evening due to flood warnings.
Rescuers were waiting for water levels to drop before entering the canyon to search for the missing.
Zion National Park is less than 32km north of the small town of Hildale, on the Utah-Arizona border, where 12 other people were killed by flash floods on Monday.
Only one person was still missing on Tuesday afternoon out of 16 people - three women and 13 children - who were in two vehicles that got hit by a wall of water and carried several hundred yards downstream.
Authorities have not identified the dead. Three people survived, all of them children.
The women and children were in an SUV and a van on a gravel road north of Hildale.
They were returning from a park when they stopped at a flooded crossing and got out to watch the raging waters, Hildale Mayor Philip Barlow said.
What they did not know was that a flash flood was brewing in the canyon above, he said. It came rushing down and engulfed their vehicles.
"We're greatly humbled by this, but we realise that this is an act of God, and this is something we can't control," said Barlow. "We have to take what we receive and do the best we can."
The deaths came as search-and-rescue teams continued to trudge through muddy streambeds in Hildale looking for people who were missing after the devastating flash flood hit the town.
With more rain in the forecast, men in helmets were perched at high points along the route, watching carefully for any more floodwaters that could suspend the search in Hildale, a secluded community that is the home base of a polygamist sect.
Along the Utah-Arizona border Tuesday, the streets of the sister towns of Hildale, Utah, and Colorado City, Arizona, were caked in red mud, and earth movers cleared the roads and piled up mounds of dirt.
As a helicopter buzzed overhead, crowds of boys in jeans and girls and women in deep-coloured prairie dresses watched the rescue effort.
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Residents called it the worst flood in memory for the community, which is south of Salt Lake City at the foot of picturesque red rock cliffs.
It was in this area at Maxwell Canyon where heavy rains sent water down Short Creek and barrelling through the towns.
The torrent was so fast, "it was taking concrete pillars and just throwing them down, just moving them like plastic", said Lorin Holm, who called the storm the heaviest in the 58 years he's lived in the community.
About three hours earlier, the National Weather Service had issued a flood warning for the area, saying: "Move to higher ground now. Act quickly to protect your life."
The raging torrents are not uncommon in an area prone to flash floods, but the volume and pace of Monday's rain was a "100-year event", said Brian McInerney, hydrologist with the National Weather Service in Salt Lake City.
Utah Governor Gary Herbert said on Tuesday that state officials were offering resources to help with the search-and-rescue effort.
Herbert is away on a trade mission in China, but he sent Lieutenant Governor Spencer Cox to the town.
Cox called it one of the worst-weather related tragedies in state history and said the Utah National Guard will send troops to assist.