ANCHORAGE, Alaska - British oil giant BP has begun cleaning up a second pipeline leak at its Prudhoe Bay operations in Alaska this week, after fluid spilled from a flow line on Wednesday.

The incident did not impact oil production in Prudhoe Bay, the largest U.S. oilfield complex, a BP spokesman said on Friday.

The leak in the 34-inch (86-cm) diameter flow line, which was discovered on Wednesday, spilled about 7,140 gallons (27,030 liters) of a watery mixture known as produced water into an operational building and an outdoor gravel area, Alaska's Department of Environmental Conservation said in a situation report late Thursday.

The spill was the second pipeline incident to affect BP's Alaska operations in less than a week, after the company found crude, gas and produced water leaking from another of its Alaskan pipelines on Sunday.

Produced water is not crude, but the often salty and oil-laced fluid can be harmful, especially if it penetrates into Alaska's fragile tundra surface.

Officials said the Wednesday spill appeared to be confined to the building and around 3,000 square feet (278 sq meters) of outdoor gravel pad, and did not affect the tundra.

The earlier spill at a pipeline near the Lisburne field briefly forced BP to shut in a small portion of North Slope oil production, which was full restored early this week.

The company is on probation after a major Alaskan pipeline spill in 2006.

The cause of both Alaskan pipeline spills this week remained unknown and under investigation, DEC said.

BP, which had a crew of more than 100 workers working to clean an oil and water in the Lisburne spill, also had begun a cleanup of the second spill, vacuuming up some of the produced water with a truck, a situation report said late Thursday.

As with the Lisburne spill, state and federal regulators will oversee the cleanup of the second spill, including officials from DEC and the U.S. Environmental Protection Agency, DEC said.

Over the next several days, the frozen produced water on a Prudhoe Bay gravel pad will be removed with jackhammers or sucked up by a vacuum truck after the area is flushed, DEC said. Crews also have been cleaning oily residue off surfaces within the manifold building.

BP shares traded up 0.4 percent Friday on the London Stock Exchange.

(Reporting by Yereth Rosen in Anchorage and Joshua Schneyer in New York; Editing by Marguerita Choy)