The 750-foot-long "Overseas Reymar," sailing under a Marshall Islands flag, was leaving the bay amid heavy fog when its starboard hull scraped one of the towers supporting the Bay Bridge.

Officials played down the incident, which occurred about 5 miles (8 km) from the Golden Gate Bridge, where the San Francisco Bay opens into the Pacific Ocean.

There were no injuries reported, according to officials.

None of the channels or ports in the San Francisco Bay were listed as shut as of Monday afternoon, and the Bay Bridge, the busy span that links San Francisco and Oakland, remained open.

The tanker struck a fender at the foot of a support tower in the bridge's western span but did not appear to otherwise damage it.

"This was basically a scrape," said Bart Ney, a California Department of Transportation spokesman. "The fender system performed as was designed. There's no damage to the bridge."

Still, the incident harked back to a similar collision in 2007, when the tanker Cosco Busan spilled more than 200,000 liters of heavy fuel oil after striking the Bay Bridge, also in the midst of heavy fog.

Coast Guard Lt. Commander Shawn Lansing said it was unclear why the Overseas Reymar veered into the bridge, but he noted that the morning fog had reduced visibility to a quarter-mile.

The collision failed to breach the hull of the vessel, which remain anchored in the bay near Alcatraz Island as of Monday afternoon as it underwent inspections.

On Sunday night, the Overseas Reymar, owned by Norton Lilly International, had safely offloaded 350,000 barrels of crude oil at Royal Dutch Shell PLC's refinery in Martinez, said Erin Hallissy, a Shell spokeswoman.

The busy waters of the San Francisco Bay are a vital conduit for California's energy market.

Nearly two-thirds of California's oil comes from out-of-state and is processed in coastal refineries. The Bay Area's five refineries represent almost half of the state's total capacity.