NEW YORK - The heatwave that began this past week in California has fuelled fires across the state, caused power outage concerns and prompted the governor to declare a state of emergency.

But the worst may be coming this holiday weekend.

Highs are expected to hit 100 deg F (37 deg C) and beyond across much of the state, with the hottest temperatures on Sunday and Monday. Many parts of the state will see excessive heat well into the week.

Warm overnight lows will only increase the heat stress, the National Weather Service warned. Those conditions will not give people a respite from the heat and will create potentially dangerous situations for vulnerable individuals.

In the San Francisco Bay Area, temperatures in the 90s (32 deg C) and 100s deg F (37 deg C) are expected over the next three days, with some locations potentially reaching 110 deg F (43 deg C), according to the weather service.

The weather service office in Sacramento predicted highs of up to 40 deg C on Saturday, 42 deg C on Sunday and 44 deg C on Monday. High temperatures are expected in the area until Wednesday.

In Southern California, the entire coastal plain will experience high temperatures in the 80s (26 deg C) and low 90s (32 deg C), while inland regions such as valleys, mountains and deserts will experience temperatures between 105 deg F (40 deg C) and 115 deg F (46 deg C), according to the weather service office in Los Angeles.

The prolonged heat has strained the electric grid in the state. As at Friday, there were 62 outages with 6,328 customers affected in Southern California.

More than 1,400 maintenance outages are scheduled in the next few weeks across the region, according to Southern California Edison. That could affect more than 65,000 customers.

While the state endures the heatwave, several fires have ignited. Although the causes of the fires are under investigation, the conditions have caused them to spread more rapidly and have sidelined some firefighters with heat-related illnesses.

The Mill fire, which broke out in Northern California on Friday, burned at least 50 structures and caused the evacuation of thousands of people in rural Siskiyou County. The fire was 20 per cent contained as at Saturday morning.

North of Los Angeles County, the Route fire has scorched 2,107 ha, injured seven firefighters and destroyed two structures after it began on Wednesday. As at Saturday morning, the fire was 71 per cent contained.

South-east of San Diego, near the Mexican border, the Border 32 fire, which also started on Wednesday, was 65 per cent contained. It has burned more than 1,780 ha. No injuries have been reported. NYTIMES