The U.S. Coast Guard says an oil tanker has leaked fuel into San Francisco Bay, creating a slick at least a mile long.

Coast Guard Petty Officer Melissa Leake says the Panamanian-flagged Dubai Star began leaking bunker fuel during a fuel transfer Friday morning.

Officials don't know exactly how much fuel has spilled into the water.

Coast Guard vessels and aircraft are on the scene about 2 1/2 miles southeast of the San Francisco-Oakland Bay Bridge.