Taiwan's naval ships are searching for the black boxes of a jumbo jet that crashed into the sea on Saturday with 225 people on board.

The China Airlines jet disintegrated in mid-air 20 minutes into a routine flight from Taipei to Hong Kong.

Relatives have been helping identify bodies

Aviation experts have put forward several theories about the causes of the crash - an internal explosion, sudden cabin de-pressurisation, a mid-air collision, or a military accident.

Taiwan's military has dismissed speculation that the Boeing 747 may have been hit by a Chinese missile.

"Communist China has denied it. We think its denial is highly credible," said a spokesman.

Bodies recovered

The spokesman added that Taiwan's military was not carrying out any exercises or missile-testing in the area at the time of the crash.

Some aviation experts have compared the accident to that of a TWA Boeing 747 passenger jet which exploded in mid-air in 1996 off New York.

An investigation report released several years later said a design flaw in the aircraft's central fuel tank was to blame.

Fishing boats and navy vessels have recovered more than 80 bodies from off the west coast of Taiwan.

"Navy ships are on their way to the area where weak signals from the black boxes were detected, but search for possible survivors is still our top priority," Transport Minister Lin Ling-san said on Monday.

Weak signals were reported to have been received from the cockpit voice recorder and the flight data recorder.

Poor safety record

Aviation Safety Council director Kay Yong said experts were trying to work out the exact locations of the recorders.

China Airlines accidents

1999 - MD11 airliner crash lands in Hong Kong, killing three people 1998 - A300-600 airliner crashes near Taipei killing all 197 on board and at least seven on ground 1994 - A300-600 crashes in Nagoya, Japan, killing 264 people 1989 - 737-200 hits mountain near Hualien, Taiwan, killing 56 people

He said military radar provided a clear picture of the plane splitting up.

"We are quite sure now that the Boeing 747-200 suffered in-flight break-up above an altitude of 30,000 feet (9,100 metres) and broke into four large parts."

Relatives of some of the victims have been flown to the scene of the disaster to help identify bodies.

Saturday's accident was China Airlines' fourth major crash in less than 10 years. The company said plane was built in 1979 and was the last of its kind in the airline's fleet.

It was reportedly its last flight for China Airlines, as it had been sold to a Thai carrier.

The government has ordered the airline to ground its remaining four Boeing 747-200 planes which are used for carrying cargo.

The crash of China Airlines flight 611 follows two major accidents in the region involving mainland Chinese airlines in the last six weeks.