BP appeared to have placed a new containment cap on its leaking well in the Gulf of Mexico, U.S. media reported on Monday.

The cap was expected to completely contain oil that has been gushing into the Gulf since the explosion of the Deepwater Horizon drilling rig in April, but tests are still needed to determine if the cap works, according to the CNN.

BP's chief operating officer Doug Suttles told a media briefing earlier in the day that the cap, a 150,000-pound (68 tons) metal stack, was very close to the well and crews would be attaching it later Monday. The work may continue throughout the day, he added.

BP removed the old cap on Saturday to make way for the installation of the new and larger one.

Suttles said it will take days to know whether the new cap can withstand the pressure of the gushing oil and siphon it through pipes to vessels on the Gulf's surface.

Once the cap is attached, the two vessels that are capturing oil from the leaking well will be shut down for crews to monitor the pressure and check the condition of the well, he said.