Japan outlined plans last week to drastically expand its defence capabilities over the next five years -- including counterstrike capability -- in response to threats from China and nuclear-armed North Korea.

"Japan is creating a serious security crisis... by adopting the new security strategy that effectively formalises the possession of preemptive strike capabilities against other countries," said the North's foreign ministry spokesperson in a statement.

"The formalisation of Japan's new line of aggression has fundamentally changed the security environment in East Asia," said the statement, which was carried by the official Korean Central News Agency (KCNA).

Tokyo will realise it has made a "wrong and very dangerous choice", the spokesman said, warning that Pyongyang "will continue to show the scale of our concern and dissatisfaction in actual action".

Japan's new strategy document warns that Moscow's military posturing in Asia and cooperation with China are "a strong security concern".

The White House said the overhaul would "strengthen and modernise" Japan's military alliance with the United States.