(adds details from press conference in Kuala Lumpur)

By Matt Siegel and Trinna Leong

SYDNEY/KUALA LUMPUR, April 16 (Reuters) - Government ministers from Australia, China and Malaysia on Thursday said they would double the search area for missing Malaysia Airlines Flight MH370 if wreckage is not found in the current target area.

No trace has been found of the Boeing 777 aircraft, which disappeared in March last year carrying 239 passengers and crew in what has become one of the greatest mysteries in aviation history. Most of the passengers were Chinese.

The extended search for the jetliner, which is believed to have crashed in the Indian Ocean off Australia's west coast, could take up to a year, officials said at a meeting in Kuala Lumpur.

Malaysian Transport Minister Liow Tiong Lai, Australian Deputy Prime Minister Warren Truss and Chinese Transport Minister Yang Chuantang pledged to double the current search area if necessary.

"Should the aircraft not be found within the current search area, ministers agreed to extend the search by an additional 60,000 square kilometres to bring the search area to 120,000 square kilometres and thereby cover the entire highest probability area identified by expert analysis," they said in a joint statement.

The second phase of the search would cost an estimated A$50 million ($38.74 million) which would be borne by Malaysia and Australia, Liow said at a press conference in Kuala Lumpur.

The total search area including the extension "would cover 95 percent of the flight path", he said.

MH370 vanished from radar screens shortly after taking off from Kuala Lumpur, bound for Beijing. Investigators believe it was flown thousands of miles off course before eventually crashing.

The search of a rugged 60,000 sq km (23,000 sq mile) patch of sea floor some 1,600 km (1,000 miles) west of the Australian city of Perth, which experts believe is the plane's most likely resting place, will likely be finished by the end of May.

Four vessels equipped with sophisticated underwater drones, have searched more than 60 percent of the previously unmapped expanse of sea floor that has been designated the highest priority.

Loss-making Malaysia Airlines, whose fortunes worsened when another of its Boeing 777's was shot down over Ukraine on July 17, killing all 298 people on board, was delisted at the end of 2014 as part of a $1.8 billion government-led restructuring. ($1 = A$1.3) (Additional reporting by Lincoln Feast in SYDNEY and Al-Zaquan Amer Hamzah in KUALA LUMPUR; Editing by Nick Macfie)