North Korea fired a missile that flew over Japan and landed in waters off the northern region of Hokkaido early Tuesday, South Korean and Japanese officials say, marking a sharp escalation of tensions on the Korean peninsula.

The test, which experts said appeared to have been an intermediate-range Hwasong 12 missile, came as U.S. and South Korean forces conduct annual military drills on the peninsula, against which North Korea strenuously objects.

Earlier this month, North Korea threatened to fire missiles into the sea near the U.S. Pacific territory of Guam after U.S. President Donald Trump warned Pyongyang would face "fire and fury" if it threatened the United States.

North Korea has conducted dozens of ballistic missile tests under leader Kim Jong-un, the most recent on Saturday, but firing projectiles over mainland Japan is rare.

"North Korea's reckless action is an unprecedented, serious and grave threat to our nation," Japanese Prime Minister Shinzo Abe told reporters.

Japan North Korea Missiles

Japanese Prime Minister Shinzo Abe speaks to journalists at his official residence in Tokyo after North Korea's firing of a projectile over Japan on Tuesday. (Kyodo News via Associated Press)

Abe said he spoke to Trump on Tuesday and they agreed to increase pressure on North Korea. Trump also said the United States was "100 per cent with Japan," Abe told reporters.

The United States, Japan and South Korea asked for a United Nations Security Council meeting to discuss the test, diplomats said. A meeting of the 15-member Security Council would be held later on Tuesday, they said.

Earlier this month, the Security Council unanimously imposed new sanctions on North Korea in response to two long-range missile launches in July.

South bombs firing range

South Korea's military said the missile was launched from near the North Korean capital, Pyongyang, just before 6 a.m. and flew 2,700 kilometres reaching an altitude of about 550 kilometres.

"We will respond strongly based on our steadfast alliance with the United States if North Korea continues nuclear and missile provocations," the South's foreign ministry said in a statement.

Four South Korean fighter jets bombed a military firing range on Tuesday after President Moon Jae-in asked the military to demonstrate capabilities to counter North Korea.

South Korea and the United States had discussed deploying additional "strategic assets" on the Korean peninsula, the presidential Blue House said in a statement, without giving any more details.

North Korea remained defiant. 

N Korea missile map

Map locating track of missile fired by North Korea on August 29. (Reuters)

"The U.S. should know that it can neither browbeat the DPRK with any economic sanctions and military threats and blackmails nor make the DPRK flinch from the road chosen by itself," North Korea's official Rodong Sinmun said later on Tuesday, using the initials of the North's official name, the Democratic People's Republic of Korea.

In 2009, North Korea fired what it said was a rocket carrying a communications satellite into orbit over Japan. The U.S., Japan and South Korea considered that launch to have been a ballistic missile test.

Japan's Chief Cabinet Secretary Yoshihide Suga said the latest North Korean missile fell into the sea 1,180 kilometres east of the Cape of Erimo on Hokkaido island.

'There's nowhere to run'

The Japanese government's J-Alert system broke into radio and TV programming, warning citizens of the possible missile. Bullet train services were temporarily halted and warnings went out over loudspeakers in towns in Hokkaido.

"I was woken by the missile alert on my cellphone," said Ayaka Nishijima, 41, an office worker from Morioka, the capital of Iwate prefecture, 300 kilometres south of Cape Erimo.

"I didn't feel prepared at all. Even if we get these alerts there's nowhere to run. It's not like we have a basement or bomb shelter, all we can do is get away from the window," she told Reuters by text message.

Global markets reacted to the escalation in tensions, buying safe-haven assets, such as gold, the Swiss franc and the Japanese yen, and selling stocks.

Japanese public broadcaster NHK reported the missile broke into three pieces and fell into waters off Hokkaido.

The Japanese military did not attempt to shoot down the missile, which passed over Japanese territory around 6:07 a.m.

Japan Defense North Korea Missiles

Lt.-Gen. Hiroaki Maehara speaks in front of Japanese Air Self Defence Force, demonstrating pre-planned training at the U.S. Yokota Air Base on the outskirts of Tokyo that occurred the same morning North Korea fired a missile over Japan. (Eugene Hoshiko/Associated Press)

In Washington, the Pentagon confirmed the missile flew over Japan but did not pose a threat to North America, and said it was gathering further information.

Australian Prime Minister Malcolm Turnbull said China, North Korea's main ally and trading partner, needed to do more.

"China has to ratchet up the pressure," Turnbull told Australian radio. "They have condemned these missiles tests like everyone else but with unique leverage comes unique responsibility."

The U.S. and South Korea are technically still at war with the North because their 1950-53 conflict ended in a truce, not a peace treaty. The North routinely says it will never give up its weapons programs, saying they are necessary to counter perceived U.S. hostility.

North Korea again asked the UN Security Council to meet to discuss the ongoing joint U.S.-South Korean military drills, according to a letter released on Monday by the North Korean mission to the United Nations.

The Aug. 25 letter to the Security Council and Secretary General Antonio Guterres from North Korean UN Ambassador Ja Song Nam described the military exercises as a "grave threat" to the Korean peninsula and international peace and security.

"It is the fair and square self-defensive right of the DPRK to cope with reckless, aggressive war manoeuvres and the U.S. would be wholly responsible for any catastrophic consequences to be entailed from the result," Ja wrote..

Similar previous requests have gone unanswered by the 15-member Security Council.

The 15-member Security Council unanimously imposed new sanctions on North Korea in response to the two July long-range missile launches.