Some 600 firefighters were battling the blaze that so far has burned some 1,200 acres (500 hectares), according to the Madera County Sheriff's Office.
With no containment in effect, the road allowing access to Yosemite from the south has been closed. However, the famous landmark remains open to the public.
As of today morning, some 1,000 people had been evacuated, with another 4,000 told they were now on standby, according to the sheriff's office. Shelters have been set up by the Red Cross for those who have to leave their homes.
The cause of the fire is under investigation.
In July, another inferno threatened a grove of famous giant sequoia trees in Yosemite, which welcomes several million visitors annually.
Last year, a gigantic blaze -- the third largest in Californian history -- tore through a swath of the park, burning more than 257,000 acres.