N.Korean test a grave threat to Japan: Abe

North Korea's decision to test-fire a ballistic missile represents a grave threat to Japan, Prime Minister Shinzo Abe says, calling on the United States and China to keep up pressure on Pyongyang.

North Korea test-fired a missile shortly after US Secretary of State Rex Tillerson warned that failure to curb Pyongyang's nuclear and ballistic missile programs could lead to "catastrophic consequences".

"Despite strong warnings by the international community, North Korea today went through its ballistic missile launch. It is a grave threat to our country. This is absolutely not acceptable. We strongly condemn such acts," Abe told reporters, speaking through a translator in London on Saturday.

US President Donald Trump has said a major conflict with North Korea was possible and that military options remain on the table.

Russia and China have warned against the use of military force.

Abe said further provocation by North Korea was "fully conceivable", calling for solidarity from the international community.

"We'd like to maintain a close coordination with the United States, our ally, to maintain a high state of alert. We'd like to be water-tight to ensure safety for our citizens," he said.

Trump has praised Chinese President Xi Jinping for his role in trying to calm the situation in North Korea. Abe welcomed Trump's engagement with Xi and said the role of China was extremely important.

"As prime minister I am focusing on China's response," he said.

"China, I hope, will play a constructive role ... it is my high expectations that China will perform its role properly."