The wildfire in Yosemite National Park, called the Oak fire, continues to burn Sunday and for the third consecutive day and has tripled its size. The blaze has burned more than 14,000 acres and thousands of local residents have been forced to evacuate Mariposa County.

The Oak fire started Friday in the Sierra Nevada foothills and is not close to being contained as of Sunday morning, according to California Fire officials. It is the third wildfire in three weeks.

California Gov. Gavin Newsom on Sunday declared a state of emergency for Mariposa County, which has a population of about 17,000 and is located about 170 miles east of San Francisco.

"The fire remained active through the night moving toward the communities of Jerseydale, Darrah, and Bootjack. Poor humidity recovery was observed overnight,” Cal Fire said in a statement.

The conditions are not expected to ease, causing greater concern for the region.

“High tree mortality and dense fuels are throughout the fire area. Fire evacuation and advisories remain in effect. Damage inspection teams are beginning their assessment of the areas affected by the fire,” the statement read.

The fires have been fueled by the 100-degree temperatures and vast winds in the highly dried-out vegetation areas. Temperatures are expected to remain in the high 90s for the rest of the week. Wind gusts on Sunday reached 16 mph.

"It really is a challenge because the amount of heat that's in this fuel. It makes it challenging to our firefighters to fight these fires," Cal Fire Battalion Chief Jon Heggie told ABC News.

The National Weather Service has warned of the extreme heat causing heat-related illness. Most of the U.S. has been under heatwave warnings throughout the past week, with over 100 million people affected.