"The ship is going to break in two in a matter of hours or days," Gibraltar's Port Affairs minister John Holiday told Spain's Cadena SER radio. He said Gibraltar had "the adequate logistics in place" to cope with whatever happened.
Holiday said the cargo would sink, but a Gibraltar government statement said the part of the ship containing some 450 tonnes of fuel was expected to remain afloat and would be towed to safety.
The Panamanian-flagged cargo ship, the New Flame has been partly submerged since it ran into a Danish tanker carrying 33,560 tonnes of unleaded gasoline on Aug. 12. The oil tanker was able to continue to the Spanish port of Algeciras.
Gibraltar, whose sovereignty is disputed by Madrid, lies at the southern tip of Spain.