Prudhoe Bay represents about half of Alaska’s oil production and about 8 percent of U.S. production, according to the U.S. Energy Information Administration.

Company officials said it would take days to shut down the oil field. Once completed, it’s expected to reduce oil field production by 400,000 barrels a day.

"We regret that it is necessary to take this action and we apologize to the nation and the State of Alaska for the adverse impacts it will cause," BP America Chairman and President Bob Malone said in a prepared statement.

Officials learned Friday that data from an internal sensing device found 16 anomalies in 12 locations in an oil transit line on the eastern side of the field. Follow-up inspections found "corrosion-related wall thinning appeared to exceed BP criteria for continued operation," the company said in a release.

That’s when workers also found a small spill, estimated to be about 4 to 5 barrels.

BP says the spill has been contained and clean up efforts are under way. State and federal officials have been informed of the decision.