Mr Key told reporters he was not satisfied airlines would be able to evacuate the New Zealand tourists stranded by increasingly violent protests at Bangkok's two main airports.
An air force Hercules was expected to leave New Zealand late on Tuesday and could be used to shuttle tourists from a Thai air force base east of Bangkok to Singapore or Malaysia.
The exact number of stranded New Zealanders was not known but it could be up to 300, he said.
The government would decide within two days whether the Hercules would fly on to Thailand to evacuate the tourists.
'But if there's a large number who want to leave, and the stand-off continues between the warring factions, then our view is we would like to deploy and get New Zealanders out,' Mr Key said.
'I think it would be irresponsible of me, as prime minister, not to act today,' he said. 'I think I've got to show some leadership.'
The Hercules would only be able to carry 65 people on each flight but two air force Boeing 757 passenger aircraft, each capable of taking 160 passengers, are both out of service for maintenance and upgrading.
A grenade attack killed an anti-government protester at Bangkok's domestic hub early on Tuesday. Political protests at the domestic and international airports have stranded about 350,000 frustrated travellers. -- AFP