BP has successfully replaced a failed blowout preventer from the top of its ruptured Macondo well in the Gulf of Mexico, US.

Retired Coast Guard Admiral Thad Allen called the equipment switch “an important milestone” towards permanently killing the leak that has discharged more than four million barrels of oil into the Gulf from 20 April to mid-July, reports Reuters.

BP said it will resume drilling the relief well over the next few days.

By mid-September the relief well will bore into the bottom of the ruptured Macondo well, which is 13,000ft beneath the seabed, and will then pump in mud and cement to permanently plug the leak.