"Today was a historic day climatologically speaking," Xinhua news agency quoted the National Weather Service Los Angeles as saying in a Facebook post on Sunday.

It said the temperature recorded in Woodland Hills broke the previous record of 48.33 degrees Celsius on July 22, 2006.

The National Weather Service said Sunday was "one of the hottest days since weather records began across much of Southwestern California".

Record or near-record temperatures were verified for a second day in a row on Sunday across the region.

"The same is true for Paso Robles where today's high of 47.22 degrees Celsius was the highest all-time temperature ever recorded at an official site in San Luis Obispo County," the agency said.

It urged California residents that extreme heat will significantly increase the risk for heat-related illnesses, and could become deadly, particularly for those working or participating in outdoor activities, as well as the elderly.

It also warned there will be an increased threat of large fires and power outages.

Cooling centres in the city of Los Angeles remained open this weekend and will be open through Monday from 12 p.m.-8 p.m. local time to help local residents escape the heat.

California declared a state of emergency on September 4 due to the dangerous heatwave.