North Korea has been briskly moving to the coast a mobile missile launcher that carries a ballistic missile, Japanese public broadcaster NHK has said.
The report also says there is increased activity at a long-range rocket launch pad on the west coast.
The mobile missile launcher is normally kept in an underground facility.
Though North Korea told UN agencies that it is launching an "earth observation satellite", fears are on the rise Pyongyang is pushing ahead with its secretive ballistic missile programme.
The US, South Korea and Japan warned Pyongyang not to go ahead with the test, and called for rougher actions against the reclusive country that pulls its diplomatic weight through weapons testing and issuing threats to neighbors.
"Should the North push ahead with the long-range missile launch ... it would have to pay the price dearly," South Korean government said in a statement.
Japanese Prime Minister Shinzo Abe condemned the North leadership, saying the launch plan was a "serious provocation.
Japan has also instructed its Self Defence Forces to shoot down any missing coming in its direction.
In 2014, North Korea had fired two mid-range, Rodong-class ballistic missiles off its east coast into the sea towards Japan.
Pyongyang's admission that it is planning a rocket launch comes after days of speculation about an imminent missile launch.