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

The test, which experts said appeared to have been a recently developed 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 four Hwasong-12 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 young 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 a grave threat to our nation," Japanese Prime Minister Shinzo Abe told reporters.

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 percent 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 Korea's military said the missile was launched from near the North Korean capital, Pyongyang, just before 6 a.m. (2100 GMT Monday) and flew 2,700 km (1,680 miles), reaching an altitude of about 550 km (340 miles).

"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.

LOUDSPEAKER WARNINGS

North Korea fired what it said was a rocket carrying a communications satellite into orbit over Japan in 2009. The United States, Japan and South Korea considered it a ballistic missile test.

"It's pretty unusual," said Jeffrey Lewis, head of the East Asia Nonproliferation Program at the Middlebury Institute of Strategic Studies in California. "North Korea's early space launches in 1998 and 2009 went over Japan, but that's not the same thing as firing a missile."

Japan's Chief Cabinet Secretary Yoshihide Suga said the missile fell into the sea 1,180 km (735 miles) east of Cape Erimo on Hokkaido.

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 km (180 miles) 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. Japan's Nikkei 225 index fell almost 1 percent to a near four-month low, while South Korea's KOSPI index was down a similar percentage.

South Korea's finance ministry said it will monitor financial markets around the clock and step in if needed.

DIALOGUE PROSPECTS?

U.S. Secretary of State Rex Tillerson appeared to make a peace overture to North Korea last week, welcoming what he called the restraint Pyongyang had shown by not conducting any tests since July.

Some experts said Kim was trying to pressure Washington to the negotiating table with its latest test.

"(North Korea) think that by exhibiting their capability, the path to dialogue will open," Masao Okonogi, professor emeritus at Japan's Keio University, said by phone from Seoul.

"That logic, however, is not understood by the rest of the world, so it's not easy," he said.

The Japanese military did not attempt to shoot down the missile, which passed over Japanese territory around 6:07 a.m. local time (2107 GMT). The missile broke into three pieces and fell into waters off Hokkaido, Japanese public broadcaster NHK reported.

Experts say defences in Japan and South Korea that are designed to hit incoming missiles would struggle to bring down a missile flying high overhead.

In Washington, the Pentagon confirmed the missile flew over Japan but said it did not pose a threat to North America and that 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 United States 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 ballistic missile and nuclear weapons programmes, saying they are necessary to counter perceived U.S. hostility.