The MV Longchamp is the third ship captured this month in the Gulf of Aden, one of the world's busiest shipping lanes.

The Longchamp, registered in the Bahamas, is managed by the German firm Bernhard Schulte Shipmanagement, which said in a statement that seven pirates boarded the tanker early on Thursday.

Spokesman Andre Delau said the ship's master had been briefly allowed to communicate with the firm and had said the crew of 12 Filipinos and one Indonesian were safe.

"We think that everything is in order, nobody is injured," he said.

No ransom demands have been made yet, the company said.

Lt Nathan Christensen, a Bahrain-based spokesman for the US 5th Fleet, said the ship was seized off the southern coast of Yemen, about 95 kilometres from the town of al-Mukalla, the capital of the Hadramaut region.

Robin Phillips, deputy director of the Bahamas maritime authority in London, said the Longchamp had been travelling in a corridor secured by EU military forces when it sent a distress signal before dawn.

"Ships and helicopters were dispatched, but they arrived too late," said Phillips, adding that gunshots could be heard over the radio. He said the ship later set a course for Somalia, to the south.

Liquefied petroleum gas is a mixture of gases used to fuel heating appliances and vehicles.