The Malaysian authorities say a new strategy will be needed if no trace of the missing airliner is found in the southern Indian Ocean by the end of May.

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Malaysia's transport minister, Liow Tiong Lai, said he remained "cautiously optimistic" that the Boeing 777 is in the area of the Indian Ocean where search efforts have been focused.

But he added: "By the end of May, if we still can`t find the plane, then we will have to go back to the drawing board."

Speaking on the eve of the first anniversary of the plane`s disappearance during a flight from Kuala Lumpur to Beijing, Mr Lai said ships looking for debris from the plane on the ocean floor off the coast of western Australia have so far covered more than 40 per cent of the 23,000 square mile search area.

On January 29, Malaysia`s government formally declared the plane an accident and said all 239 people on board were presumed dead.

Australia, Malaysia and China are due to meet next month to discuss the search efforts.

Mr Lai said an interim report on the investigation, a requirement under international civil aviation regulations, will be released to the public on Sunday.

He outlined measures his government had already undertaken a year since the disaster, including plans to upgrade radar system to cope with bigger traffic volume and a new tracking system on Malaysia Airlines flights which sends aircraft data every 15 minutes, instead of previous 30 to 40 minutes.

MH370 vigil (Getty)

The plane dropped off civilian radar when its transponder and other equipment were switched off shortly after takeoff from Kuala Lumpur, but was tracked for some time by Malaysia`s military radar as it headed south across the country towards the Indian Ocean.

Read more: Flight MH370 one year on: what we know - and don't know

There are countless theories about what happened to flight MH370.

One UK aviation expert has said the plane was "deliberately flown off course" and will probably never be found.

David Learmount, operations and safety editor of Flightglobal publication, said: "We are no nearer discovering exactly what happened to this plane than we were a year ago. But all the evidence - and I mean all - suggests the aircraft went to a spot where its computers would never have taken it.

"It looks as if there was some kind of deliberate act. The plane changed direction dramatically. It did a U-turn and went somewhere that makes absolutely no sense whatsoever."

He added: "The plane ducked and dived. If the pilots, for some reason, had become incapacitated then the plane would have flown on along its planned route.

"We have got to get used to the fact that we may never find this plane. The Australians have said the search can't be kept up for ever."