Los Angeles residents have been left incredulous after heavy rains and flash flooding hit southern California as tropical storm Hilary made landfall on Sunday.

Locals posted images and videos on social media of large, rapidly-moving flows along the Los Angeles River, which usually only carries a small amount of water in the typically hot, dry region.

“For those of you who have never lived in L.A., this image is genuinely nuts,” Matthew Chapman wrote on X, formerly Twitter. “The L.A. ‘River’ is barely even a river most of the time. Usually it’s either a tiny trickle of water at the bottom of a concrete bed, or just completely dry.”

The National Weather Service has issued a flash flood warning for the area, and in its latest forecast discussion wrote that in southwestern U.S. states, the “ongoing and potentially historic amount of rainfall” is expected to cause “life-threatening to locally catastrophic” flooding including landslides.

Vehicles splash up water during heavy rains from Tropical Storm Hilary, in south Los Angeles, California, on August 20, 2023. Hurricane Hilary weakened to a tropical storm the same day as it barreled up Mexico’s Pacific coast, but was still likely to bring life-threatening flooding to the typically arid southwestern United States, forecasters said.
ROBYN BECK/AFP via Getty Images

Ahead of the storm’s arrival, on Saturday, California Governor Gavin Newsom declared an emergency. Ventura County firefighters were on Sunday night searching for one person trapped in the Santa Clara River, with a further two rescued.

This is a developing story and will be updated with further information.