A containment cap newly placed over a ruptured undersea well is collecting some 1,000 barrels of crude a day, the U.S. commander for the Gulf of Mexico oil spill said Friday.

The device is designed to corral "90-plus percent" of the oil, BP's chief operating officer Doug Suttles told CNN earlier on Friday.

Government scientists had estimated that 12,000 to 19,000 barrels of oil could be spewing into sea per day.

The amount of runaway oil could decrease when BP closes vents to maximize the oil corralled, U.S. Coast Guard Admiral Thad Allen told reporters on a conference call.

The successful deployment of the cap followed BP's several failed attempts to curb the oil spill which has so far contaminated at least 225 kilometers of coastline, stopped new deep-water drilling in the Gulf of Mexico and forced the closure of a third of its fishing areas.

Suttles told CNN earlier Friday that the cap "should work." " I'd like to see up capture 90-plus percent of this flow," he said. "I think that's possible with this design."

BP's plan is to use the cap to trap most of the oil and siphon it to a tanker on the Gulf's surface until the company completes two relief wells to plug the leak. The wells are expected to be finished by mid-August.

The cap was placed over the leak following the cutting and removal of the riser pipe from the top of the BOP's lower marine riser package (LMRP).

Like its attempts, BP said this operation also has never before been deployed at 5,000 feet under water and that "the containment system's efficiency, continued operation, and ability to contain the oil and gas cannot be assured".