An oil well on the ocean floor beneath a drilling rig that exploded and sank into the Gulf of Mexico began spewing oil on Saturday, the U.S. Coast Guard said.

The well, 5,000 feet beneath the ocean surface, was leaking about 1,000 barrels per day of oil, a Coast Guard spokeswoman said, in what the agency called a “very serious spill.” Remote underwater vehicles detected oil leaking from the riser and drill pipe, the spokeswoman said.

“We are classifying this as a very serious spill and we are using all our resources to help contain it,” Coast Guard Petty Officer Connie Terrell said.