VANDENBERG AIR FORCE BASE, Calif. >> Crews are working to surround a wildfire at a central California Air Force base before it threatens heavily used launch pads used to send satellites into space.

The blaze at Vandenberg Air Force Base expanded to the south Tuesday as it grew to more than 16 square miles. It is 20 percent contained.

Voluntary evacuation orders are in place for about 400 residents of the San Miguelito Canyon area just off the base near Lompoc.

There is no word of any structures threatened on the sprawling base, much of which is undeveloped and rugged mountain land.

Nearly 800 firefighters were deployed to corral the fire when it broke out Sunday in a remote canyon. The cause is under investigation.

Col. Paul Nosek said on the base’s Facebook page that there is currently no threat to the space launch complex.