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.

The move came as North Korea warned foreigners living in South Korea to consider evacuating, saying they risked personal injury should a conflict break out.

A spokesman for Japan's military says two Patriot Advanced Capability-3 surface-to-air missile launchers were stationed at the defence ministry in Tokyo before dawn.

"We are proceeding with measures including deployment of PAC-3 as we are on alert," defence minister Itsunori Onodera said.

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

So far, Tokyo's response to the threats emanating from Pyongyang has been low key and the missile deployments are the most visible sign yet that the country rattled.

"The government is making utmost efforts to protect our people's lives and ensure their safety," prime minister Shinzo Abe told reporters on Tuesday morning [local time].

"As North Korea keeps making provocative comments, Japan, cooperating with relevant countries, will do what we have to do.

"For the moment, the most important thing is to implement sanctions under the UN Security Council resolutions."

PAC-3 batteries will also be installed in the semi-tropical island chain of Okinawa.

North Korean leader Kim Jong Un inspects a Korean People's Army unit at an undisclosed location. ( Supplied: Korean Central News Agency (KCNA), file photo )

Mr Onodera says Okinawa is "the place that is most effective in responding to emergencies...so we should deploy the unit in Okinawa on a permanent basis".

Defence officials say Japan's armed forces are authorised to shoot down any North Korean missile headed towards its territory.

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

Fresh warnings

Tokyo's moves came just before North Korea told foreigners living in the South to consider evacuating.

"In the event of war, we don't want foreigners living in South Korea to get hurt," said a statement attributed to the North's Asia-Pacific Peace Committee.

The statement, carried by the official Korean Central News Agency, urged "all foreign organisations, companies and tourists to work out measures for evacuation".

Earlier, North Korea said 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.

The mid-range missiles mobilised by the North are reported to be untested Musudan models with an estimated range of around 3,000 kilometres that could theoretically be pushed to 4,000km with a lighter payload.

That would cover any target in South Korea and Japan, and possibly even US military bases on the Pacific island of Guam.

The North has no proven inter-continental ballistic missile capability that would enable it to strike more distant US targets, and many experts say it is unlikely it can mount a nuclear warhead on a mid-range missile.

North Korea's Musudan missile range: the inner circle covers a 3,000km radius and the outer 4,000km.

AFP