Japan plans to deploy advanced interceptor missiles at its air bases across the nation to counter the threat of North Korea's ballistic missiles, Kyodo News reported on Saturday.

The deployment of Patriot Advanced Capability-3 interceptor missiles will be under new five-year defence policy guidelines to be announced as early as next week, Kyodo said, quoting government and defence officials.

The PAC-3 missile system, designed to shoot down an incoming missile from the ground, will be deployed to all six of the Air Self-Defense Force's air defense missile groups from three at present, Kyodo said.

The move comes amid heightened tensions on the Korean Peninsula following North Korea's artillery attack on a South Korean island last month, and China's rapid military build-up and increasing naval activity.

On Friday, Japan and the United States finished their biggest-ever joint military exercise in a powerful display of firepower after a US and South Korean show of force to pressure Pyongyang.

The new guidelines will also stipulate equipping all six Aegis destroyers with Standard Missile-3 interceptors, while increasing the number of submarines from 16 to 22 for enhanced vigilance in southwestern Japan.

The number of escort ships will be increased from 47 to 48 while the number of major operational aircraft will be trimmed from 350 to 340 due in part to the larger size of transport planes.

The guidelines will call for a reduction in tanks and artillery as part of efforts to shift the focus from land operations to maritime defence, local media reported.

As for the closely watched issue of the Ground Self-Defense Force's troop strength, the government is in the final stages of deciding whether to maintain it at the current 155,000 or reduce it to 151,000 at most, Kyodo added.