Investigators trying to locate the missing Malaysian jet expanded the search range to 6,000 miles, stretching from Kazakhstan to the southern Indian Ocean.

The move followed Malaysian Prime Minister Najib Razak's revelation that a faint signal had been received from the aeroplane seven hours after takeoff, indicating that it could have been flown anywhere within that vast area.

French experts arriving in Kuala Lumpur to lend expertise gained during the two-year search for an Air France jet that crashed in the Atlantic Ocean in 2009 said they had been able to rely on distress signals.

However, that vital tool is missing in the Malaysia Airlines mystery because flight MH370's communications were deliberately severed before its disappearance over a week ago.

"It's very different from the Air France case. The Malaysian situation is much more difficult," said Jean-Paul Troadec, a special adviser to France's aviation accident investigation bureau.

Malaysian authorities said that the jet carrying 239 people was intentionally diverted from its flight path during an overnight flight from Kuala Lumpur to Beijing on March 8 and flew off-course for several hours.

Suspicion has fallen on the pilots, although officials insist that they are looking into everyone aboard the flight.

Malaysian Airlines chief executive Ahmad Jauhari Yahya said that an initial investigation indicated that co-pilot Fariq Abdul Hamid had spoken the flight's last recorded words - "All right, good night" - to ground controllers.