Japan has deployed Patriot missiles in its capital as it readies to defend the 30 million people who live in greater Tokyo from any North Korean attack, an official said Tuesday.

Two Patriot Advanced Capability-3 surface-to-air missile launchers had been stationed at the defence ministry in Tokyo before dawn, a ministry spokesman said.

Local reports said PAC-3 will be deployed in another two locations in the greater Tokyo area.

Batteries will also be installed in the semi-tropical island chain of Okinawa, Defence Minister Itsunori Onodera told a television programme broadcast Monday.

He said Okinawa was "the place that is most effective in responding to emergencies... so we should deploy the unit Okinawa on a permanent basis".

Japan's armed forces are authorised to shoot down any North Korean missile headed towards its territory, a defence ministry spokesman said Monday.

In addition to the PAC-3s, Aegis destroyers equipped with sea-based interceptor missiles have been deployed in the Sea of Japan, the defence official said.

Tokyo's moves came as North Korea said Monday it was withdrawing all workers and suspending operations at a lucrative joint industrial zone with South Korea, with reports of heightened activity at the North's nuclear test site and at a missile battery.

North Korea's bellicose rhetoric has reached fever pitch in recent weeks, with near-daily threats of attacks on US military bases including in Japan and South Korea in response to ongoing South Korea-US military exercises.

Intelligence reports suggest Pyongyang has readied two mid-range missiles on mobile launchers on its east coast and plans a test-firing before the April 15 birthday of late founding leader Kim Il-Sung.