The search for missing Malaysia Airlines flight MH370 has turned up the unexpected discovery of a shipwreck on the sea floor of the southern Indian Ocean.

Flight MH370 disappeared without a trace in March last year while on a flight from Kuala Lumpur to Beijing with 239 people on board, but is believed to have crashed in the Indian Ocean off Australia's west coast.

Four vessels owned by Dutch engineering firm Fugro, equipped with sophisticated underwater drones, have already searched more than 60 per cent of the previously unmapped 60,000-square-kilometre expanse of sea floor.

Last month the search area was doubled.

This week the Joint Agency Coordination Centre said the wreck of a ship had been found about 4 kilometres below the surface and more than 1,000kms off Western Australia.

At this stage, authorities know little about the wreck, but said the debris was man-made and that images would be handed to marine archaeologists for identification.

WA Maritime Museum curator Michael McCarthy said the wreck was likely to be a 19th century cargo ship.

"The best we can do at the moment is a mid-to late 19th century wooden hull, iron sailing ship and of unknown origin but of European-style build," he said.

Professor McCarthy said the find was not unexpected, but not knowing where the ship came from or its intended destination would make identifying it difficult.

"There are hundreds of ships lost in our world's oceans over time, through old age, cyclones, typhoons and one would expect this to occur," he said.

"You have these vessels say from a place like Fremantle which takes a notice of its lost ships, but you will find other countries that probably haven't kept the same records, [so] we are in a bit of trouble trying to do that."

The search for the missing Malaysia Airlines plane continues.