Los Angeles, California (CNN) -- Rain pounded water-logged Los Angeles on Thursday, and Mayor Antonio Villaraigosa said more than 300 city residents were ordered to evacuate because of the threat of mudslides.
"We continue to urge the public who live in these areas to evacuate, to heed the warnings of our police officers and firefighters, our first responders, who are there to protect your public safety," the mayor said.
Just over 500 Los Angeles County residents who were advised to flee their homes earlier had done so by Thursday morning, said Capt. Sam Padilla of the Los Angeles County Fire Department.
The latest storm is part of a series that began Monday, drenching communities up and down the coast. Some areas have received more than 12 inches of rain this week, the National Weather Service reported. Flash flood watches were in effect Thursday night for Southern California, as well as central Arizona and southern Utah.
"While the worst of the last few storms is behind us, there still is a significant threat from thundershowers that are forming off the coast," Villaraigosa said at a news conference Thursday night, warning of the potential for lightning, hail and water spouts.
Los Angeles had four swift-water rescue and two urban search-and-rescue teams on standby to deal with potential flooding, according to the mayor, who said more were available if needed. There were three swift-water rescues Wednesday, according to Padilla.
No relief from the wet weather is expected until the weekend, increasing the threat of mudslides in communities nestled below hills that were stripped of trees and vegetation during 2009 wildfires.
Villaraigosa said the brunt of the storm was supposed to hit by 6 p.m. Rainfall totals of 1 to 4 inches are expected across coastal sections of California with isolated additional rainfall amounts of 7 inches possible, forecasters said.
The rains are the result of El Niño, a warm ocean current from the South Pacific, according to CNN meteorologist Chad Myers.
In coastal Pacifica, south of San Francisco, a huge mudslide left an apartment building teetering on the edge of a cliff overlooking the Pacific Ocean, CNN's Dan Simon reported. He said the four apartments in the building were evacuated, and quoted an engineer saying the building could topple into the water at any time. TV crews could be near the structure only briefly.
One man complained about being told to leave his Southern California home.
"You're talking about blocking us out of here for five days, evacuating until next week," he said to CNN affiliate KABC-TV in Los Angeles. "You know what, that's too many days, that's a huge inconvenience. I understand they're looking out for our safety ... but I'm not out driving around. I'm staying put."
Villaraigosa said Thursday that U.S. geologists, sanitation workers and street maintenance workers will head into threatened regions Friday morning to determine whether it is safe for residents to return to their homes.
In the mountains of Southern California, the storms brought heavy snow, closing Interstate 15 at Cajon Pass and the Grapevine section of Interstate 5 for a time, the California Highway Patrol reported Thursday.
Heavy snowfall remains in the forecast for the higher elevations in the Sierra Nevada, southeastern Utah, southwestern Colorado and southeastern Arizona. More than 73 inches of snow has fallen in Chagoopa Plateau, California, since Sunday and more than 35 inches in parts of Arizona.
CNN's Sean Morris contributed to this report.