China today demanded that Malaysia keep providing more thorough and accurate information about a Malaysia Airlines flight that was on its way to Beijing when it disappeared a week ago, after Malaysia said the plane was deliberately diverted.

Investigators believe someone aboard the airliner deliberately shut off its communications and tracking systems, turned the plane around and flew for nearly seven hours after it vanished, Prime Minister Najib Razak said earlier in the day.

Najib said analysis of the plane's last communication with satellites placed it in one of two corridors: a northern stretch from northern Thailand to the border of Kazakhstan and

Turkmenistan, or a southern stretch from Indonesia to the southern Indian Ocean.

China's Foreign Ministry said it "paid very close attention" to the news.

"We demand that the Malaysian side continue to provide to China more thorough, accurate information," the ministry said, adding that it was sending a technical team to Malaysia to help with the probe.

"We will also get in touch with relevant countries and international organisations to understand, study and determine (what happened)."

The ministry repeated a demand for Malaysia to step up its search, and asked it to involve more countries in the effort.

"China will also promptly adjust its search deployments and ask countries which may be involved to provide assistance," it added.

Separately, China's Defence Ministry said that two warships which had been searching in the Gulf of Thailand were on their way to the Malacca Strait, one of the world's busiest waterways.

The fate of the Malaysian Airlines Boeing 777-200ER has been shrouded in mystery since it disappeared off Malaysia's east coast less than an hour into a March 8 scheduled flight from Kuala Lumpur to Beijing.

But investigators have increasingly focused on the possibility it was flown off-course by the pilot or co-pilot, or someone else on board with detailed knowledge of how to fly and navigate a large commercial aircraft.

Frantic family members

China has repeatedly asked Malaysia for clear information, and to provide answers for the increasingly frantic family members of Chinese passengers aboard the aircraft.

Wen Wancheng, whose son was on the plane, said he felt no clearer about what had really happened.

"They ought to be sharing information publicly and transparently with everyone in the world," he told reporters at a Beijing hotel where the relatives had gathered.

"It's the responsibility of Malaysia and Malaysian Airlines to deal with the missing plane."

Another family member, who declined to give his name, said he was glad at least of progress in the probe, and held out hope the passengers were still alive.

"In the overall view of the situation, it's good news. This means that there's still hope that our relatives are alive," he told reporters.

There were 153 Chinese nationals on board the ill-fated fight.