Japan began deploying on Friday its ground-based Patriot Advanced Capability-3 interceptors, with units leaving Iruma air base northwest of Tokyo to be positioned closer to the political and financial centres of Tokyo.
According to the North Korean government, the rocket's planned trajectory should take it over Japan.
But officials in Pyongyang have cautioned that the rocket's first booster would land in the Sea of Japan, while the second stage would drop into the Pacific Ocean between Japan and Hawaii.
While the North Korean government says the rocket launch is aimed at space development, there are international concerns that it is a cover for a long-range missile test.
Russia has urged Pyongyang to refrain from its planned rocket launch and called for dialogue with the North's government.
Japan has previously asserted that it will attempt to shoot down any missile or debris that threatens to hit its territory.
|The US has pledged to punish Pyongyang if it carries out the launch [AFP]
But officials say the chances that debris will fall on its territory were slim and have called on the public not to panic.
Pyongyang said it would regard any attempt to shoot down or otherwise interfere with its rocket as an act of war.
Japan's constitution does not allow it to intercept a missile if it is clearly heading elsewhere.
Japan, South Korea and the US have pledged to punish Pyongyang if it goes ahead with the launch, condemning the act as a violation of a Security Council resolution passed in 2006.
The resolution prohibits North Korea from conducting long-range missile tests, or using a rocket to send a satellite into space.
In its only previous test flight in 2006, the Taepodong-2 was deliberately destroyed after failing just after launch.