Midpines, United States - California firefighters were making slow progress Monday battling a raging wildfire near Yosemite National Park that will force some residents to evacuate with “just the shirts on their back,” officials said.

The latest blaze -- which has already forced thousands to evacuate -- comes as much of the United States remain in the grip of a sweltering heat wave.

The Oak Fire in Mariposa County has burned 16,791 acres (6.795 hectares) and is so far 10 percent contained, Cal Fire, the state fire department, said Monday.

“What we’re seeing on this fire is very indicative of what we’ve seen in fires throughout California, in the West over the last two years,” Jon Heggie, a Cal Fire battalion chief, told CNN. “These fires are burning with just such a velocity and intensity it makes it extremely challenging and extremely dangerous for both the public and the firefighters,” Heggie said. “It’s moving so quickly it’s not giving people a lot of time and they sometimes are just going to have to evacuate with just the shirts on their back,” he said.

The Oak Fire has forced the evacuation of several thousand people so far, officials said, and the hot and dry conditions and steep, rugged terrain are complicating firefighting efforts.

More than 2,000 firefighters backed by 17 helicopters have been deployed against the Oak Fire, which broke out on Friday near the vast Yosemite National Park in central California.