San Francisco, Jul 4 (IANS): Wildfires spread in Northern California amid heatwaves, causing thousands to evacuate, officials have said.

About 70 miles (113km) north of California's capital Sacramento, crews have been battling a wildfire in Butte County, Xinhua news agency reported.

Approximately 28,000 residents were under the evacuation order near Oroville on Wednesday due to the fast-moving fire, according to the Department of Forestry and Fire Protection of California (CAL FIRE).

The blaze, dubbed the Thompson Fire, broke out before Tuesday noon and grew to more than 3 square miles (10.6 square kilometres) by Wednesday morning, with zero containment.

Smoke from the fires has been blown towards Sacramento with hazy skies reportedly seen above the city.

The largest current blaze, the Basin Fire, was 26 per cent contained after burning some 22 square miles (56 square kilometres) of the Sierra National Forest in eastern Fresno County since it was sparked on June 26.

California's heat was expected to spread from north to south over the week, focusing on interior areas such as the Sacramento and San Joaquin valleys and the southern deserts.

Sacramento is under an excessive heat warning expected to last until Sunday night, with temperatures forecasted to reach between 105 degrees and 115 degrees (40.5 and 46.1 Celsius).

There were 2,934 Wildfires in California, burning 139,590 Acres (565 square kilometres), as of Wednesday morning, CAL FIRE said.

Red flag fire warnings were issued across the state. The state governor's office announced late Tuesday that federal funding had been approved to help with firefighting efforts.

The utility Pacific Gas & Electric implemented public safety power shutoffs in parts of 10 counties to prevent wildfires from being ignited by downed or damaged electrical wires.