Japan on Thursday dispatched three destroyers to waters over which North Korea says its satellite-bearing rocket will travel.
Television footage showed three Aegis destroyers armed with SM-3 missile interceptors leaving their base in Sasebo, some 900 kilometres west of Tokyo.
They were reportedly bound for the East China Sea and the Sea of Japan, a stretch of water known to Koreans as the East Sea.
Separately, a naval ship carrying PAC-3 (Patriot Advanced Capability-3) ballistic missiles arrived in the Okinawan island of Miyakojima on Thursday morning.
Television footage showed Self-Defence Force units unloading the missiles from the vessel at a harbour on the island, which lies on the expected flight path of the rocket.
In Tokyo, the defence ministry has deployed another PAC-3 battery at its headquarters as part of its effort to intercept anything headed towards the Japanese mainland.
Prime Minister Yoshihiko Noda’s cabinet plans to hold a security meeting on Friday to issue an advance order to shoot down the rocket if it looks set to fall on Japanese territory, Jiji Press reported.
Immediate confirmation of the reports was not available.
The communist North announced on Saturday that it would launch a rocket between December 10 and 22 – its second long-range rocket launch this year after a much-hyped but botched attempt in April.
Japan took similar defensive steps at the time.
It has reportedly notified neighbours including Japan of the trajectory of the planned launch.
Pyongyang insists its efforts are directed solely at the peaceful use of space, but many in the international community say the satellite launch is a poorly disguised missile test.
Washington and Seoul urged Pyongyang to scrap the launch while Tokyo postponed talks due this week with North Korea.