Nuclear-armed North Korea fired a ballistic missile over Japan yesterday in a major escalation that triggered global alarm and a furious response from the government in Tokyo.

A visibly unsettled Japanese Prime Minister Shinzo Abe said it was an "unprecedented, serious and grave threat", while the UN Security Council called an emergency meeting at Tokyo and Washington's request.

Sirens blared out and text messages were fired off across northern Japan warning people in the missile's flight path to take cover.

Trains were delayed as passengers were urged to seek shelter inside stations.

"All lines are experiencing disruption," said one sign on Sapporo's metro system. "Reason: Ballistic missile launch."

US President Donald Trump warned yesterday that "all options" are on the table after North Korea fired the missile over Japan.

"Threatening and destabilizing actions only increase the North Korean regime's isolation in the region and among all nations of the world," Trump said, in a statement released by the White House.

"All options are on the table."

Trump said the world "has received North Korea's latest message loud and clear: this regime has signaled its contempt for its neighbors, for all members of the United Nations, and for minimum standards of acceptable international behavior."

But North Korean ambassador Han Tae-Song, addressing the UN Conference on Disarmament in Geneva, said his country had the right to react to ongoing US-South Korean military exercises.

"Now that the US has openly declared its hostile intention towards DPR Korea by raising joint aggressive military exercises despite repeated warnings, Han said.

"My country has every reason to respond with tough counter-measures as an exercise of its rights to self-defense," he warned.

Washington, Han declared, would be responsible for "the catastrophic consequences" that may result from heightened tensions on the Korean peninsula.

The North always condemns the annual Ulchi Freedom Guardian exercise and other joint drills as a rehearsal for invasion, while Seoul and Washington say they are purely defensive.

SIRENS BLARE IN JAPAN

Sirens blared out and text messages were fired off across northern Japan warning people in the missile's flight path to take cover.

Trains were delayed as passengers were urged to seek shelter inside stations.

"All lines are experiencing disruption," said one sign on Sapporo's metro system. "Reason: Ballistic missile launch."

The last time a North Korean rocket overflew Japan was in 2009, when Pyongyang conducted what it said it was a satellite launch. Washington, Seoul and Tokyo said it was really an intercontinental ballistic missile test.

TIPPING POINT

Abe called the overflight an "outrageous act" that "greatly damages regional peace and security".

In a 40-minute telephone call with Trump, Abe said the two leaders agreed to "further strengthen pressure against North Korea."