An El Niño-strengthened storm brought widespread rain to drought-stricken California on Tuesday, triggering flooding that clogged roadways, and authorities warned residents about possible mud slides.

The National Weather Service (NWS) has issued flash flood watches for much of the coast from San Diego to San Francisco and said storms would linger through Friday. The service forecast widespread rain and mountain snow.

Emily Thornton, a NWS meteorologist in Los Angeles, said Tuesday's storm was the strongest thus far of the El Niño season, which she said is expected to last into spring.

"It's definitely the biggest rainmaker we've had," Thornton said, adding that another storm would replace it on Wednesday.

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The weather service warned of flooding on urban roads, as well as flash floods and mud flows that could hit areas recently ravaged by wildfires.

There were no immediate reports of weather-related injuries, but California Highway Patrol said four cars were damaged when large rocks fell from a cliff onto the Pacific Coast Highway in Malibu Canyon.

The Los Angeles Fire Department said it had made several water rescues by Tuesday afternoon.

Southbound lanes of the 101 freeway, a major roadway that runs the length of California, were also briefly closed near Santa Barbara due to mud and water, officials said.

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Police in Glendora, a Los Angeles suburb, closed a road due to flooding and debris flowing onto the street. Pictures provided by the department showed a few inches of muddy water snarling traffic.

Further north, the Bay Area county of Santa Cruz saw heavy rainfall, and the San Francisco Chronicle newspaper said vehicle accidents were reported across the greater Bay Area.

California is in its fourth year of a drought that has cost the state's agricultural economy $1.84 billion, according to the University of California, Davis.

The El Niño phenomenon, characterized by a warming of the Pacific Ocean that often brings precipitation to California, is expected to help ease the drought over the next few months, but experts caution the state's woes are far from over.