A dangerous heat wave is expected to hit Southern California this weekend with an increased serious risk of wildfires, the US National Weather Service said.

"Dangerously hot conditions this Labor Day weekend over southwest California. Temperatures may reach all time highs. Heat illness can kill," Xinhua news agency quoted the National Weather Service Los Angeles as saying in a tweet on Thursday.

It urged people to check in on loved ones who are especially vulnerable, such as the very young, very old, outdoor enthusiasts and workers.

The agency warned that high pressure building over the West Coast this week will lead to an increase in temperatures each day through the weekend and dangerous heat is expected across all areas from Friday through September 7, with the hottest day on Sunday.

Sunday will be "a brutal day" with most highs in the valleys and deserts coming in between 43.3 and 46.1 degrees Celsius, the agency said in a forecast.

An excessive heat warning issued by the National Weather Service will go into effect from 10 a.m. Friday until 8 p.m. on September 7 in some regions in Southern California.

"There is a high risk for heat illness along with heightened fire weather concerns during this time.

"Near normal temperatures will return by the end of next week," the agency added.