US firefighters have started to bring under control California’s wildfire, the largest so far this year, halting its eastward expansion towards nearby Yosemite National Park, while thousands of people remained under evacuation orders.

Here is what to know about it:

What happened and when?

*  The so-called “Oak Fire” in central California broke out on Friday and is raging while parts of the United States swelter through a heatwave.

*  The fire in Mariposa County has engulfed 17,241 acres (6,977 hectares) – more than half the size of Paris.

*  Nearly 3,000 firefighters backed by 24 helicopters have been deployed near the southwestern edge of Yosemite National Park.

Where did the Oak Fire start?

*  The fire started in the foothills of the Sierra Nevada, west of Yosemite National Park, in Mariposa county.

*  The actual cause remains under investigation, authorities said.

Is it safe now? Where is the Oak Fire moving?

*  According to authorities, the fire department started controlling the fire on Monday. In a statement, they said, “helicopters control dropped 300,000 gallons (1.3 million litres) of water on the fire.”

*  It was 16 percent contained, up from 10 percent contained on Monday morning, and 3,700 people had been evacuated.

*  The fire continues to move in a northeasterly direction into the Sierra National Forest but no longer towards Yosemite, some 16 kilometres (10 miles) away.

*  Fire restrictions and closures near the area remain in place. California Department of Forestry and Fire Protection (Cal Fire) said 55 residential, commercial and other structures had been destroyed.

Why is the ‘megafire’ spreading?

*  In recent years, California and other parts of the western US have been ravaged by huge and fast-moving wildfires, driven by years of drought and a warming climate.

*  “This is a direct result of what is climate change,” Jon Heggie, a Cal Fire battalion chief, told broadcaster CNN.

*  “You can’t have a 10-year drought in California and expect things to be the same,” he said. “That drought is what drives what we are calling megafires,” he added.

*  Jonathan Pierce, a spokesman for the fire department, said low humidity and high temperatures were stoking the blaze, worsened by the high number of dead trees and steep slopes in the area.

*  Extreme temperatures could be seen elsewhere in the country, as 60 people in the US were under a heat advisory on Monday.

Photos:

A helicopter drops water while battling the Oak Fire in Mariposa County on Sunday

A forest is incinerated by the Oak Fire near Midpines, northeast of Mariposa, California, on July 23

A bulldozer passes firefighters cutting vegetation to broaden a fireline at the Oak Fire near Mariposa, California, on July 25