Wellington  - New Zealand Prime Minister John Key announced Tuesday that he had ordered an air force transport plane to fly to South-east Asia in preparation for a mercy mission to rescue New Zealanders stranded in Bangkok.

Key told a news conference that the Hercules C130 would go to Singapore or Malaysia on Wednesday and be put on stand by to fly to the Thai military airbase of U-Tapao, about 150 kilometres east of Bangkok.

He said he was not satisfied that up to 300 New Zealanders believed to be stranded by the anti-government protest which has closed Bangkok's international airport for a week would be able to leave by commercial carriers.

The government has come under increasing pressure from families of New Zealanders stuck in Bangkok to help get them home, following Australia's move to charter planes from Qantas Airways for its citizens in Thailand.

No final decision has been made, but Key said the Hercules would fly to the region so that it would be close to U-Tapao, where it could pick up New Zealanders shuttled there from Bangkok's international airport.

The Hercules transport can carry only up to 65 passengers, but the Royal New Zealand Air Force's two Boeing 757 passenger planes are both being upgraded in the United States.