Residents of the Oakland hills north of Interstate Highway 580 and Edwards Drive were being evacuated Tuesday afternoon because of a four-alarm grass fire, police and fire officials said.

As of shortly after 1 p.m., police said they were evacuating the streets of Bayview Drive, Skyview Drive, Ridgemont Drive and Viewcrest Drive and houses in the 13650 block of Campus Drive.

Police were asking people to avoid the area.

About 50 homes were threatened by the fire, Cal Fire officials said.

The officials said as of about 1 p.m. that the fire has burned 20 acres. It was spreading at a moderate rate.

The fire was reported at 12:13 p.m. near Mountain Boulevard and Edwards Avenue.

When fire officials reported the fire on Twitter, they said it was spreading rapidly on a steep hill.

The National Weather Service issued a red flag warning Tuesday through Wednesday afternoon for the East Bay hills because of dry weather conditions that pose a high risk of wildfires.