Authorities in Gibraltar say an operation to pump fuel out of a stricken gas tanker is under way after it began leaking oil into the sea.
The OS 35 developed a serious leak after it collided with another vessel off the southern tip of the Iberian Peninsula on Monday.
Divers have since sealed the source of the leak but the environmental impact and the quantity of oil spilt were not immediately clear.
Chief Minister of Gibraltar Fabian Picardo told Spanish media earlier on Thursday that the operation to remove about 500 tonnes of fuel from the ship’s tanks should take roughly 50 hours using the ship’s own pumps.
Officials said early on Friday that 80 per cent of the diesel on the ship had been removed but that about 180 tonnes of heavy fuel is still on board.
The spokesman, who was not authorised to be named publicly, said the ship had been carrying 250 tonnes of diesel, and still had 183 tonnes of heavy fuel oil and 27 tonnes of lubricant oil in its tanks.
The heavy fuel oil is potentially more damaging to the environment and more difficult to extract, raising concerns in Spain and Gibraltar over local marine life and tourism.
The usually busy port of Gibraltar remains closed, but the neighbouring Algeciras port in Spain is fully operational.
Mayor of nearby La Linea de la Concepcion, Juan Franco, said fuel from the leak had been pushed by winds and currents towards a nearby beach.
“What has entered is a worrying spillage but it is not a tragedy,” Mr Franco said. He said the most important issue was to remove the remaining fuel oil on the tanker safely.
The collision happened when the OS 35 was attempting to exit the bay.
Bulk carriers are vessels dedicated to transporting solid goods, such as grain, and the fuel on board is that used by the ship itself.
The liquefied natural gas tanker suffered no significant damage.
Gibraltar's busy port has been mostly closed since the accident.
The territory, measuring only 6.8 square kilometres, overlooks the only entrance to the Mediterranean from the Atlantic Ocean, putting it on the shipping route to the Middle East via the Suez Canal.