* Missile flies over Hokkaido, far into Pacific
* S.Korea estimates missile flew about 3,700 km, could reach Guam
* U.S. military detects one intermediate range ballistic missile
* Launch comes after biggest N.Korea nuclear test this month
* Japan, Australia condemn provocative, reckless action (Adds detail on warnings and missile, U.S. general on nuclear test, Trump briefed, paragraphs 4-9, 12-13, 20)
SEOUL/TOKYO, Sept 15 (Reuters) - North Korea fired a missile that flew over Japan's northern Hokkaido far out into the Pacific Ocean on Friday, South Korean and Japanese officials said, further ratcheting up tensions after Pyongyang's recent test of its most powerful nuclear bomb.
The missile flew over Japan and landed in the Pacific about 2,000 km (1,240 miles) east of Hokkaido, Japan's Chief Cabinet Secretary Yoshihide Suga told reporters in a hastily organised media conference.
"These repeated provocations on the part of North Korea are impermissible and we protest in the strongest words," Suga said.
Warning announcements about the missile blared around 7 a.m. (2200 GMT Thursday) in the town of Kamaishi, northern Japan, footage from national broadcaster NHK showed.
The missile reached an altitude of about 770 km (480 miles) and flew for about 19 minutes over a distance of about 3,700 km (2,300 miles), according to South Korea's military - far enough to reach the U.S. Pacific territory of Guam.
The U.S. military said soon after that it had detected a single intermediate range ballistic missile.
North Korea has launched dozens of missiles under young leader Kim Jong Un as it accelerates a weapons programme designed to give it the ability to target the United States with a powerful, nuclear-tipped missile.
"This rocket has meaning in that North Korea is pushing towards technological completion of its missiles and that North Korea may be feeling some pressure that they need to show the international community something," said Yang Uk, a senior research fellow at the Korea Defence and Security Forum.
Last month, North Korea fired a missile from similar area near the capital Pyongyang that also flew over Hokkaido into the ocean. Two tests in July were for long-range intercontinental ballistic missiles capable of reaching at least parts of the U.S. mainland.
"ASHES AND DARKNESS"
South Korea said it had fired a missile test into the sea to coincide with North Korea's launch and the presidential Blue House has called an urgent National Security Council meeting. Japan also convened a National Security Council meeting.
The North's launch came a day after Pyongyang threatened to sink Japan and reduce the United States to "ashes and darkness" for supporting a U.N. Security Council resolution imposing new sanctions against it for its Sept. 3 nuclear test, its sixth and most powerful by far.
The U.S. general who oversees America's nuclear forces said on Thursday he was making the assumption that the test was in fact a hydrogen bomb, as Pyongyang had claimed, based on the size of the blast.
"I'm assuming it was a hydrogen bomb," said Air Force General John Hyten, head of the U.S. military's Strategic Command. "I have to make that assumption as a military officer," Hyten told a small group of reporters who were accompanying Defense Secretary Jim Mattis on a trip to Hyten's headquarters in Nebraska.
The North accuses the United States, which has 28,500 troops in South Korea, of planning to invade and regularly threatens to destroy it and its Asian allies.
Australia, a strong and vocal ally of the United States, quickly condemned the launch.
"This is another dangerous, reckless, criminal act by the North Korean regime, threatening the stability of the region and the world and we condemn it, utterly," Australian Prime Minister Malcolm Turnbull said in an interview with Sky News on Friday.
"This is a sign, I believe, of their frustration at the increased sanctions on North Korea, recently imposed by the Security Council. It's a sign that the sanctions are working," he said.
The United Nations Security Council voted unanimously on a U.S.-drafted resolution and a new round of sanctions on Monday, banning North Korea's textile exports and capping fuel supplies.
The U.S. dollar fell sharply against the safe-haven yen and Swiss franc in early Asian hours in response to the launch, although losses were quickly pared in very jittery trade.
U.S. President Donald Trump had been briefed on the latest launch, the White House said.
Trump has vowed that North Korea will never be allowed to threaten the United States with a nuclear-tipped missile, but has also asked China to do more to rein in its neighbour. China in turn favours an international response to the problem.
The United States and South Korea are technically still at war with North Korea because the 1950-53 Korean conflict ended with a truce and not a peace treaty.
(Reporting by Jack Kim and Christine Kim in SEOUL and Hideyuki Sano in TOKYO; Additional reporting by Mohammad Zargham in WASHINGTON; Editing by Lincoln Feast and Paul Tait)