Japan's defence minister has said Tokyo could shoot down a North Korean rocket if it enters Japanese airspace, according to media reports.

"I am considering giving an order to intercept it," Naoki Tanaka told parliament on Monday. Such an order would be subject to approval by the prime minister, he added.

Two Japanese newspapers, Asahi and Yomiuri, reported on Tuesday that Japan was considering deploying several Aegis-class warships and surface-to-air PAC-3 Patriot missiles to take down the rocket.

Nuclear-armed North Korea says April's long-range rocket launch is to carry a satellite into space, but the plan has prompted scepticism among regional governments.