SYDNEY • An underwater sonar vehicle used in the search for the missing Malaysia Airlines plane MH370 sank after hitting an undersea volcano, Australian officials said yesterday.

The "towfish", which was pulled by a search ship and fitted with survey instruments, plunged to the bottom of the remote southern Indian Ocean on Sunday.

Australia's Joint Agency Coordination Centre (JACC), in a statement, said: "The towfish collided with a mud volcano, which rises 2,200m from the sea floor, resulting in the vehicle's tow cable breaking.

"The towfish and 4,500m of cable became separated from the vessel, and are now resting on the sea floor."

Australia is leading the search for the Boeing 777 that vanished on March 8, 2014, en route from Kuala Lumpur to Beijing, with 239 people onboard. The aircraft is thought to have crashed after diverting from its course but, so far, the undersea hunt has found no sign of it.

In July, a 2m-long wing part called a flaperon washed up on a beach on the Indian Ocean island of Reunion, marking the first concrete evidence that MH370 met a tragic end.

A barnacle-encrusted piece of metal found in Thailand at the weekend prompted speculation that it too could be from MH370 but ocean-current modelling suggests it is unlikely to be from the missing plane.

Officials said there were no injuries to the crew onboard the search ship Fugro Discovery.

The ship yesterday was on its way to the Western Australian port of Fremantle so a replacement cable could be fitted, in a bid to recover the towfish. The journey is expected to take about a week.

"During the journey, the spare towfish on board the Fugro Discovery will be readied for future search activities," the JACC said.

The key instruments in the towfish are side-scan sonar and multi-beam echo sounders that look for man-made objects on the sea floor.

AGENCE FRANCE-PRESSE