TOKYO - A visibly shaken Japanese Prime Minister Shinzo Abe met reporters outside his residence early Tuesday morning (Aug 29), minutes after North Korea fired a ballistic missile that flew over Hokkaido into the Pacific.

"We will immediately collect and analyse information, and we will make every effort to protect the lives of the people firmly," he said in a brief statement at about 6.20am (5.20am in Singapore).

Soon after, he spoke with US President Donald Trump on the phone for 40 minutes, with the two leaders discussing their future response and reaffirming that their positions are in "perfect alignment", for the need for pressure against the bellicose state to be ramped up.

"The missile launch this time marks an unprecedented, grave threat and Japan and US will press for an emergency United Nations Security Council meeting. Our stance that pressure needs to be ramped up further against the North Korea is in 'perfect alignment," Mr Abe said following his phone call with Mr Trump.

Mr Trump said the US was "100 per cent with Japan" and he showed a strong commitment to Tokyo's defence, Mr Abe added.

At the request of the US, Japan and South Korea, the United Nations Security Council (UNSC) will hold an emergency meeting on Tuesday to discuss North Korea's latest ballistic missile launch.

North Korea has fired rockets across the Japanese mainland into the Pacific in 1998, and then in 2009. Like the two prior instances, it did not give any prior warning to Japanese authorities this time, potentially endangering aircrafts or ships operating in the area.

As of 10.30am, there have not been any reports of damage to any aircraft or ship, nor any damage to any Japanese property.

The latest provocation comes despite a marked dialing down of rhetoric between US and North Korea, which earlier this month had engaged in a war of words. It came after Japan last week imposed unilateral sanctions against Pyongyang, on top of the tougher international sanctions that have been passed by the United Nations.

North Korean leader Kim Jong Un threatened to fire a missile into waters around the US territory of Guam, after Mr Trump vowed to unleash "fire and fury like the world has never seen" if provoked. It also comes just a week after Mr Trump said he believed that Mr Kim was "starting to respect us".

Kobe University security expert Tosh Minohara said that as history shows, any silence is "really the calm before the storm".

He added: "The less rhetoric you hear, the more the situation is actually becoming serious and indeed, this past week or two there has been less rhetoric."

"The threat has gone to the next stage."

South Korea's presidential Blue House said on Tuesday the US is considering deploying 'strategic' defence capabilities to South Korea in response to the latest provocation.

General Jeong Kyeong Doo, chairman of South Korea's Joint Chiefs of Staff, and his American counterpart General Joseph Dunford agreed to take related measures at the earliest possible date, which apparently include the temporary dispatch of US strategic assets like long-range bombers to the Korean peninsula, reported South Korea's Yonhap news agency.

Four South Korean F-15K fighter jets staged a live-bombing drill on Tuesday, dropping eight MK-84 bombs - each weighing about a ton - at a simulated target at the Pilseung Range in the eastern province of Gangwon, reported Yonhap.

They hit the target accurately, it said, adding the practice was aimed at sharpening the capability of completely destroying "the enemy's leadership" in case of an emergency.

South Korea also released on Tuesday footage of the testing its new ballistic missile that has a range of 800 km.

At 5.58am on Tuesday morning (local time), North Korea fired a Hwasong-12 intermediate range ballistic missile that flew more than 2,700km and reached an altitude of 550km. It crossed Hokkaido at about 6.06am, before breaking up into three parts and falling in the Pacific Ocean at 6.12am, 1,180km to the east of Cape Erimo.

Japanese defence minister Itsunori Onodera told reporters on Tuesday that by the rocket's flight path, it was believed that the missile, launched from Sunan, near Pyongyang, was not fired on a "lofted trajectory".

Tokyo has lodged a protest "in the strongest terms" with North Korea through its embassy in Beijing, Japanese foreign minister Taro Kono said.

He said that regardless of whether the missiles are fired over Japan's north or its south - as Mr Kim said he would do when he made his threat against Guam - it would amount to the "same level of provocation for Japan".

He added: "I'm not in the position to comment on what North Korea is thinking. But if they strike south, it would amount to a reasonable provocation towards the US, which might in turn retaliate. In consideration of that , I think the North might be a little scared of that."

Lt. Gen. Hiroaki Maehara, the commander of the Japan Air Self-Defense Force's Air Defense Command, said the armed forces did not try to shoot down the missile on Tuesday because they did not detect a threat to Japanese territory.

But when the government detected the launch and followed the path of the missile, it warned citizens in its path to take cover - just in case any parts fell on Japan.

Dr Minohara said that the "scary" fact was how the missile had split into three, which could mean either of two things: (i) it was a rocket failure; or more seriously; (ii) it was a multiple independently targetable reentry vehicle (MIRV). The latter refers to a ballistic missile comprising several warheads, with each capable of being aimed at different targets.

Speaking to the CNN, missile scientist David Wright said: "It is a big deal that they overflew Japan, which they have carefully avoided doing for a number of years, even though it forced them to test missiles on highly lofted trajectories, and forced them to launch their satellites to the south, which is less efficient than launching to the east (due to the Earth's rotational motion).

"This will make it more difficult for the US to get Japanese support for diplomacy, unfortunately, at exactly the time when the situation is heating up," said Dr Wright, co-director of the Global Security Program at the Union of Concerned Scientists.

Four minutes after Tuesday's launch, at 6.02am, the J-Alert warning system was also triggered in 12 northern and north-eastern prefectures from Hokkaido to Fukushima, with residents urged to take cover in a sturdy building as far as possible.

Bullet trains that ply north-eastern Japan also ground to a halt before being given an all-clear to resume operations, resulting in delayed service that lasted for hours.

At the JR Sapporo station - the hub of Hokkaido's main city - a notice on the electric bulletin board at the ticket gate on Tuesday morning read: "There is a delay or a cancellation in train services in both directions due to a missile launch by North Korea."

Public broadcaster NHK reported a pervasive sense of unease in the affected areas.

An 82-year-old fisherman who was working at a port in Tsuruoka City in the north-eastern Yamagata prefecture said: "Because the disaster prevention siren was an eerier sound that is different from usual alerts, I felt something bad was happening. I am worried, even if the missiles did not fall."