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.
Two Patriot Advanced Capability-3 surface-to-air missile launchers had been stationed at the defence ministry in Tokyo before dawn on Tuesday, a ministry spokesman said, while Defence Minister Itsunori Onodera said "we are proceeding with measures including deployment of PAC-3 as we are on alert".
Local reports said PAC-3 will be deployed in another two locations in the greater Tokyo area.
Tokyo's response thus far to the threats emanating from Pyongyang has been low key and Tuesday's moves are the most visible yet that it is 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.
"As North Korea keeps making provocative comments, Japan, co-operating 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, Onodera told a television program broadcast on Monday.
He said Okinawa was "the place that is most effective in responding to emergencies ... so we should deploy the unit in 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.
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.