Southern California sizzled on Friday in record-breaking heat from the desert to the sea, with widespread highs and withering conditions that stoked wildfires.

Officials urged people to take advantage of cooling centres in libraries and other facilities and to watch out for the elderly and very young, warning that minor heat-related illnesses can worsen quickly.

Sidewalks and outdoor lunch tables were left to the blazing sun.

"There are no people," said Gloria Aguilar, 37, a food vendor in the Los Angeles piñata district. "Because it's too hot, and they want to stay inside the house. We sell more water than the food."

Construction workers carry large bottles of water during a break in the blistering days heat in downtown Los Angeles as Southern California baked under a heat wave. Photo / AP
Construction workers carry large bottles of water during a break in the blistering days heat in downtown Los Angeles as Southern California baked under a heat wave. Photo / AP

Firefighters worked in extreme temperatures as they battled outbreaks of wildfires, including a destructive blaze in the San Diego County community of Alpine and another that spread from a truck fire on Interstate 15 in Cajon Pass east of Los Angeles.

Torrid conditions were expected to last through Saturday before easing a bit Sunday.

The heat was being produced by a "humongous" dome of high pressure that was also spreading oppressive conditions into parts of Arizona, Nevada and Utah, the National Weather Service said.

"Today will be one for the record books," the Los Angeles region weather office said before sunrise — and within a few hours records began to fall.

In downtown Los Angeles, it was only 10.15am when the mercury topped the July 6 mark of 34.4 Celsius set in 1992 and kept on rising, hitting 37.7 Celsius before noon and continuing upward.

LA's Woodland Hills neighborhood was a record 46.1 Celsius by early afternoon, just a few degrees behind the 48 punishing the aptly named community of Thermal in the low desert southeast of Palm Springs.

Southeast of Los Angeles in Orange County, Los Alamitos Race Course cancelled daytime racing after two races because of the heat.

The offshore flow of air pushing back the normal moderating influence of the Pacific Ocean had produced startling early morning temperatures: At 3am, it was 36.6C in Gaviota on the Santa Barbara County coast about 201km west of Los Angeles, the weather service said.


While beaches offered relief from the furnace-like conditions, forecasters warned that a lingering south swell from former Hurricane Fabio would continue to combine with a local northwest swell to produce dangerous rip currents and the possibility of sneaker waves.

Residents toughing it out in the valleys around Los Angeles and in the inland region to the east faced the possibility of unhealthy air quality. Air pollution regulators said the conditions were likely to produce an atmospheric inversion that would increase ground-level ozone, which is linked to a host of respiratory troubles ranging from trouble breathing to asthma attacks.

The highest fire danger stretched from Los Angeles County westward into several counties up the coast where a north wind added another element to the mix of hot, dry air and parched vegetation. Elsewhere, the fire risk was characterized as elevated.

An additional threat was likely to develop by Sunday with the arrival of seasonal monsoonal moisture and the possibility of thunderstorms.

"Any lighting strike is going to be a concern," said Alex Tardy, a meteorologist with National Weather Service in San Diego.

- AP