The Japanese government said it was in the air for 50 minutes
North Korea has fired an intercontinental ballistic missile, US military sources have confirmed.
The intercontinental ballistic missile flew east, from South Pyongan Province, reports Yonhap.
South Korean Military Joint Chiefs of Staff said the United States and South Korea are analysing details of the launch.
A US government source confirmed the launch, which was detected at 6.30pm GMT. The Pentagon says there is no threat to the USA or its allies.
The Japanese government said it was in the air for 50 minutes. It is reported to have travelled about 1000km on a "lofted trajectory" before coming down in the Sea of Japan.
South Korea's military says the ICBM had an altitude of 4,500km.
Pentagon spokesman Colonel Robert Manning said: "We detected a probable missile launch from North Korea. We are in the process of assessing the situation and will provide additional details when available."
The South Korean military said it conducted a missile firing exercise shortly after the launch.
According to a defence ministry source, it may have landed in Japan's exclusive economic zone.
The Japanese Prime Minister Shinzo Abe has ordered an emergency meeting of his Cabinet over the launch. US President Donald Trump was briefed while still flying from India.
It is the first launch since September 15th, when North Korea fired an intermediate ballistic missile. It also comes one week after President Trump put the secretive nation back on the list of countries that support terrorism.
North Korea denounced the decision calling it a "serious provocation and violent infringement".
Earlier today, Yonhap reported that South Korea and the United States were "closely watching" the possibility of "provocative acts" from the north.
The Japanese government was on alert after radio signals suggested North Korea may be preparing for a launch.
South Korea's unification minister said on Tuesday that North Korea may announce the completion of its nuclear weapons programme in 2018.
According to Yonhap News, Cho Myoung-gyon said: "North Korea has been developing its nuclear weapons at a faster-than-expected pace. We cannot rule out the possibility that North Korea could announce its completion of a clear force within one year."
Earlier this month, the North Korean ambassador to the United Nations said the country could not abandon its programme, as it was a deterrent to the USA.
Han Tae Song ruled out negotiations with America as long as joint US-South Korea military exercises continued.