TOKYO, JAPAN - Japan's air force is prepared to deploy its ground-based missile interceptors if the defence minister gives an order, its chief said on Friday, amid reports North Korea may test-launch a long-range missile in weeks.

Pyongyang fired a long-range rocket over Japan in April, saying it was putting a satellite in orbit, but which was widely viewed as a long-range missile test. Last week, the North tested a nuclear device and test-fired several short-range missiles, further raising tensions in the region.

Asked whether Japan is preparing to deploy its ground-based Patriot Advanced Capability-3 (PAC-3) interceptors, a defence ministry spokesman quoted air force chief Kenichiro Hokazono as telling a news conference that it is still gathering information on North Korea's moves.

'As was the case last time, the air self defence force is getting ready to swiftly deploy when the minister gives a deployment order,' Hokazono added.

Tokyo deployed interceptors ahead of North Korea's long-range rocket launch in April, whose planned trajectory showed that it would go over Japan. It ended up not launching any interceptors.

U.S. and South Korean reports have said the North has shown indications of shipping an intercontinental ballistic missile - theoretically capable of reaching Alaska and Hawaii and military targets in Guam - toward a test site on its east coast.

Hokazono said the air force plans to deploy within three hours after the minister's order, the spokesman said.

Japan, which has two destroyers equipped with Standard Missile-3 (SM-3) interceptors and six ground-based PAC-3 interceptors, is forbidden by its pacifist constitution to intercept a missile if it is clearly heading elsewhere.

But the defence minister can order the military to destroy any debris that poses a threat to Japan.

Besides a possible long-range missile test, North Korea is preparing to fire a mid-range missile, capable of hitting most of Japan, South Korea's Yonhap news agency reported earlier this week.