TOKYO • Japan has stepped up preparations for a possible North Korean missile strike, with the government publishing information online about what to do in the event of an attack and briefing local officials on counter-measures.

When a warning is issued, residents have only 10 minutes to flee to safety before impact, reported The Japan Times.

Japan has a system known as J-Alert which, under the Cabinet Secretariat, is designed to get the word out about an imminent missile attack.

Increased efforts to make contingency plans in response to growing public concern will likely accelerate the government and the ruling Liberal Democratic Party's push for an upgraded ballistic missile defence system.

In the event that a J-Alert is sounded, any information will be broadcast via satellite, telephone and cyberspace to disaster management officials at the local level.

Subsequently, local governments will relay warnings via outdoor loudspeaker systems, emergency broadcast channels on cable television, FM radio broadcasts and cellphone alerts.

The advice posted on the Cabinet Secretariat's Civil Protection Portal site recommends that citizens take cover inside sturdy buildings or underground shopping areas in case a ballistic missile is headed for an area, reported the Asahi Shimbun.

People without access to such structures are told to lie on the ground behind objects, while those inside buildings are advised to stay away from windows. Students in schools have been told to remain in their classrooms and get under their desks.

The number of views on the Civil Protection Portal site has surged to about 2.6 million this month from 450,000 last month, after beginning a gradual climb in February last year, reported The Japan Times.

The government's vigilance has intensified since North Korea test-launched four ballistic missiles almost simultaneously on March 6, three of which fell within Japan's exclusive economic zone after travelling about 1,000km.