Divers sealed two tank vents that leaked fuel from a bulk carrier that was damaged and beached after a collision off the British enclave of Gibraltar on the southern tip of Spain, local authorities said on Thursday.

The hull of the bulk carrier OS 35 broke after the collision with an LNG tanker and started leaking fuel oil on Wednesday, but the vessel has not broken into two parts.

"The Captain of the Port confirmed that the leak of low sulphur fuel oil from the tank vents is fully under control," the Gibraltar government said in a statement.

The LNG tanker was not significantly affected by the collision, according to local authorities.

The Gibraltar Port Authority is working with a Spanish marine rescue crew to collect a small amount of fuel oil that escaped the perimeter of a boom installed soon after Tuesday's collision, as well as to skim the fuel that has remained inside the boom.

At the same time the authority is ramping up efforts to start pumping the fuel oil, diesel and lube oil from the vessel.

Chief Minister of Gibraltar Fabian Picardo told Spanish broadcaster TVE earlier on Thursday the operation to remove around 500 tonnes of the fuel from the ship's tanks should take around 50 hours using the ship's own pumps.

The Gibraltar Port was partly closed to focus its resources on dealing with the emergency, but some operations, such as the arrival of a cruise ship on Thursday, have been allowed to proceed.