Canberra, January 25, AZERTAC

An underwater sonar vehicle used in the search for missing Malaysia Airlines plane MH370 has now been lost to the deep ocean floor after hitting an undersea volcano, Australian officials said on Monday.

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

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

"The towfish and 4,500 metres 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 the undersea hunt has so far found no sign of it.

Last July, a two-metre-long wing part known as a flaperon washed up on a beach on the Indian Ocean island of Reunion, giving the first firm evidence that the flight met a tragic end.

Australian officials said there were no injuries to crew in Sunday's incident onboard the Fugro Discovery and it was thought that the towfish could be recovered.