The move against a half dozen organisations and a couple of individuals comes days after Washington expanded its own punitive measures against Chinese and Russian firms, as well as people linked to Pyongyang.

The US move drew an angry response from Beijing, North Korea's key ally, while Japanese media said Friday that Namibia has been tightening its links to the North in recent years.

"We will continue to make strong calls (for North Korea) to take actions toward denuclearisation," Yoshihide Suga, the Japanese government's top spokesman, told a regular press briefing.

"Now is the time to apply pressure," he added.

The sanctions are aimed at disrupting the flow of cash funding North Korean weapons programmes, which are in violation of United Nations resolutions.

Japan has previously frozen the assets of entities and individuals involved in natural resources and research work related to Pyongyang's nuclear and missile development programmes.

The US and its allies, particularly Japan and South Korea, have been on high alert in recent months as North Korea carried out successive missile tests.

Tensions have eased since North Korean leader Kim Jong-Un pulled back from a plan to send a salvo of missiles towards the US Pacific territory of Guam.

But Pyongyang Wednesday disclosed significant technological advances and ambitious plans to further improve its missile capabilities.

US President Donald Trump, like his predecessors, has called on China to play more active roles in convincing North Korea to stop threatening its neighbours and the US.

But China has so far been lukewarm on the idea, preferring to address the issue through long-stalled talks.

On Friday, China hit out the new Japanese sanctions.

"We firmly oppose any other unilateral sanction outside the framework of the UN Security Council, in particular those targeting Chinese entities and individuals," Chinese foreign ministry spokeswoman Hua Chunying told a regular press briefing in Beijing.

"We urge the Japanese side to stop this and if it insists on doing this wilfully, it must accept the consequences," she added, without elaborating.

China backed new United Nations sanctions against North Korea this month and has announced that it was upholding them by banning imports of iron, iron ore and seafood from its neighbour.

Beijing had already suspended imports of North Korean coal in February.