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SAN FRANCISCO (CBS 5 / AP / BCN) ― The U.S. Coast Guard said an oil tanker spilled hundreds of gallons of bunker fuel into San Francisco Bay on Friday, creating an oil slick up to two miles long and about 200 yards wide.

However, officials indicated none of the fuel had made it to shore so far, there were no immediate reports of oiled wildlife and crews were working to minimize the environmental harm.

"They're doing an admirable job containing the spill," said San Francisco Mayor Gavin Newsom. "Environmental concerns are the primary focus of our efforts right now."

City officials did advise residents though to avoid contact with the bay waters.

They said people should refrain from swimming in the Bay and stay away from beaches. Fishing around Treasure Island, Yerba Buena Island and from the east side of San Francisco Pier 39 to Candlestick Point was also not advised.

The oil leak happened when a fuel line ruptured during a fuel transfer on the Panamanian-flagged Dubai Star, according to Coast Guard Petty Officer Melissa Leake.

The Coast Guard said it responded quickly after the spill was reported at 6:48 a.m. at Anchorage Nine, about 2 1/2 miles southeast of the San Francisco-Oakland Bay Bridge.

The crew of the ship, which carries oil and other chemicals, realized there was a mechanical failure and cut off the source of the spill, Coast Guard Lt. Steve Youde said.

Officials indicated it was unknown exactly how much fuel had spilled into the water, but they estimated it was hundreds of gallons.

Friday's calm weather out on the Bay was helping in the cleanup operation, Coast Guard Capt. Paul Gugg said.

"The weather is very cooperative," he said. "There's never a good day for an oil spill, but if you've got to have one, this is the kind of weather you'd want."

Newsom said booms were quickly deployed to contain the oil slick and additional booms were protecting Treasure and Yerba Buena islands.

The Coast Guard sent seven booming vessels to environmentally sensitive areas, and put down 1,100 feet of booming material around the boat, Gugg said.

National Response Corp., a nonprofit company specializing in oil-spill cleanup, was contracted by the Coast Guard to cleanup the spill.

A 100-yard security zone was established around the vessel and spill site, and local oil spills response organizations were also notified about the incident.

Staffers from the UC Davis Wildlife Health Center and its partner organizations in the Bay Area were among those groups that responded to the scene of the spill to assess the situation and collect any oiled animals that might be found. 

California Department of Fish and Game Lt. Rob Roberts said initial assessments indicated that no animals were affected, but he noted that the local seabirds were still a primary concern.

"We don't know if any birds are affected, but we're certainly looking into it," added Paul Kelway, a spokesman for the International Bird Rescue Research Center in Fairfield.

Officials wanted to assure the public that Friday's oil spill was not nearly as bad as the disastrous 2007 Cosco Busan oil spill.

Newsom said officials learned from that spill which leaked 53,000 gallons of fuel into the bay, killed 2,400 birds and caused $70 million in damage to beaches and the fishing industry.

Monique Moyer, executive director of the Port of San Francisco, said the main difference between the two incidents was that oil had not reached land in this case.

Staff from the San Francisco Bay Regional Water Quality Control Board were monitoring the Friday spill's potential impact on the environment, and ensuring that any damage is mitigated, said Executive Officer Bruce Wolfe.

The Regional Water Board would also be responsible for assessing any fines that might result from the spill and from any violations of state and federal clean water laws.

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