Media playback is unsupported on your device Media caption The BBC's Richard Westcott tracks the final communications of MH370

China says it has started searching its territory for missing Malaysia Airlines flight MH370, while Australia has narrowed its search area in the south.

Efforts to find the aircraft are focusing on two vast air corridors north and south of the plane's last known location.

China said no evidence of terror links had been found in Chinese passengers.

The plane went missing on 8 March with 239 people on board. Some 26 countries are involved in search efforts.

Malaysia says the plane was intentionally diverted and could have flown on either a northern or southern arc from its last known position in the Malacca Straits.

Search efforts are focused on two corridors - one stretching from the border of Kazakhstan and Turkmenistan to northern Thailand, and another from Indonesia to the Indian Ocean.

Investigators are looking into the possibility that the aircraft's crew - or other individuals on the plane - were involved in its disappearance.

A total of 153 Chinese nationals were on board the missing aircraft, which was flying from Kuala Lumpur to Beijing.

Chinese Ambassador to Malaysia Huang Huikang said that search and rescue operations in the Chinese territories of the northern corridor had begun, Xinhua news agency reported.

Based on background checks, there was no evidence to suggest that the mainland Chinese passengers on the plane were involved in hijacking or launching a terror attack, Mr Huang added.

China said it had also deployed 21 satellites to help with the search.

'Needle in a haystack'

Meanwhile, the Australian Maritime Safety Authority (Amsa) said it had narrowed down its search area in the southern Indian Ocean based on satellite data and analysis of the aircraft's possible movements.

However, Amsa said the search area was still vast.

"A needle in a haystack remains a good analogy," Amsa Emergency Response General Manager John Young said, adding that there was a "difficult" task ahead.

"The sheer size of the search area poses a huge challenge - the search area is more than 600,000 square kilometres (230,000 sq miles)," he added.

Late on Monday, US officials said the US navy ship USS Kidd had been taken off the search because the enlarged search area meant that "long-range patrol aircraft" were "more suited" to the mission.

The move was made "in consultation with the Malaysian government", officials said in a statement. USS Kidd had searched the Andaman Sea but found "no debris or wreckage associated with an aircraft", they added.

Image copyright Reuters Image caption Australia is leading search efforts along the southern arc from the plane's last known location

Image copyright AFP Image caption Relatives of the passengers have been waiting desperately for updates for days

Image copyright Reuters Image caption Well-wishers have left messages of support on a board at the airport in Kuala Lumpur

The US says it is using patrol aircraft including the P-8A Poseidon and P-3C Orion to continue search efforts, with the P-8 taking part in search efforts in the south corridor.

'Breaches rejected'

The Malaysia Airlines plane left Kuala Lumpur at 00:40 local time (16:40 GMT) on 8 March. The last transmission from the plane's Aircraft and Communications Addressing and Reporting System (ACARS) was received at 01:07.

A transmission expected 30 minutes later did not come through, Malaysia Airlines Chief Executive Ahmad Jauhari Yahy told reporters. Officials believe the communications systems were deliberately disabled.

The last words from the plane - "all right, good night" - were believed to have been said by co-pilot Fariq Abdul Hamid to air traffic controllers at 01:19 as the plane left Malaysian airspace.

It then disappeared from air traffic controllers' screens at 01:21, when it was over the South China Sea, but was last spotted by military radar at 02:15 over the Malacca Straits - the opposite direction from its planned flight path.

Satellite communication at 08:11 showed that the plane could have continued flying for a further seven hours in a northern or southern arc.

Several countries have already rejected the suggestion that their airspace might have been breached, the BBC's Jonah Fisher in Kuala Lumpur reports.

After 11 days of a huge multinational investigation and search, almost all options for the fate of flight MH370 are still being considered, our correspondent adds.