China has worked out a plan for the search and rescue of the missing Malaysia Airlines jet.
The national Maritime Search and Rescue Center says the plan involves four patrol and rescue vessels and two naval warships.
The search range of the six ships has also been clarified.
Chinese warship Mianyang and a marine police vessel have joined the massive search, which involves some 40 ships and 34 aircraft from nine different nations.
The Chinese government has also sent a working group to Malaysia composed of officials from several ministries.
At the latest press conference in Kuala Lumpur, Malaysian civil aviation chief Azharuddin Abdul Rahman says the fate of the missing plane remains a mystery.
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"Unfortunately, ladies and gentlemen, we have not found anything that appears to be objects from the aircraft, let alone the aircraft...It's an unprecedented missing aircraft mystery as you can put it."
He says all reported sightings of debris from the plane in the seas south of Vietnam were unconfirmed.
The official also says authorities have not ruled out hijacking as a cause of the plane's disappearance.
154 Chinese nationals are among the 239 people on board the Boeing 777-200.