A strike team from the San Francisco Fire Department was preparing Friday to head to the Yosemite area to help battle the expanding Rim Fire.
The fire has crossed into Yosemite National Park as of Friday morning since it started Aug. 24 at nearby Stanislaus National Forest, U.S. Forest Service officials said.
Scroll down to see video of the Rim Fire.
As of Friday morning, the blaze has charred more 105,000 acres -- nearly doubling in size since Thursday night. Sixteen structures have been destroyed and 4,500 other structures are threatened.
Among the many Bay Area fire crews dispatched to the area, 22 San Francisco Fire Department members were heading to the blaze Friday fire spokeswoman Mindy Talmadge said. Five engines were scheduled to leave Friday afternoon from 19th and Folsom streets. A full strike team was requested and includes a team leader and an assistant leader, Talmadge said.
Other San Francisco fire officials and an engine crew arrived at the Rim Fire Wednesday night, she said.
Earlier this week, fire crews were dispatched to Tuolumne County to help monitor San Francisco resources such as powerhouses and other water supply and hydroelectrical equipment.
The Hetch Hetchy Reservoir is located in Yosemite National Park and supplies water to millions of Bay Area residents and business.
There have been no reports of ash or other issues with the water supply and delivery system because of the fire, San Francisco Public Utilities Commission officials said.
The fire was last reported to be 12 miles downstream from the reservoir, SFPUC officials said.
Some electrical power equipment has been shut down because it is in the fire zone, but power is still being generated at one running turbine, officials said.
The cause of the fire is under investigation. It was only 2 percent contained with more than 2,000 firefighters responding as of late Friday morning, according to the forest service.
Road closures were still in effect Friday, including a shutdown of state Highway 120 that leads into Yosemite, and evacuations have been ordered at nearby communities.