The Japanese Government warned people not to approach any debris or other suspicious-looking material, a reflection of the fact that North Korean missiles sometimes break up in flight.
Japan's chief cabinet secretary, Yoshihide Suga, condemned the latest launch in "the strongest terms possible" and reiterated that Japan would "not tolerate" North Korea's actions. But Japan did not try to shoot down the missile.
South Korea, however, immediately fired one of its Hyunmoo-II missiles 250km into the sea - the same distance it would have had to travel to reach the Sunan airfield.
In Washington, the White House said President Donald Trump was briefed on the latest North Korean missile launch by his chief of staff, John Kelly.
The missile did not pose a threat to North America or to the US territory of Guam, the U.S. Pacific Command said. The Pacific island of Guam is home to large US Air Force and Navy bases and was the target of North Korea's recent rhetorical threats.
Yesterday's launch appeared similar to the previous launch, on August 29. On that day, North Korea fired a Hwasong-12 - an intermediate-range ballistic missile technically capable of flying 5000km, enough to reach Guam - from the Sunan airfield. But it also flew to the east, over Hokkaido and into the Pacific Ocean, rather than on a southward path toward Guam.
Analysts said that after testing its missiles by firing them straight up and having them crash into the sea between the Korean Peninsula and Japan, North Korea was apparently testing its missiles' flight on a normal trajectory without crossing a "red line" of aiming at the United States.
On Thursday, a North Korean state agency had issued an alarming threat to what it offensively called the "wicked Japs". "The four islands of the [Japanese] archipelago should be sunken into the sea by [our] nuclear bomb," a spokesman for the Korea Asia-Pacific Peace Committee said in a statement carried by the official news agency. Hokkaido is the northernmost of Japan's four main islands. "Japan is no longer needed to exist near us," the committee spokesman said.
This is the first missile launch since North Korea conducted a huge nuclear test on September 3, which analysts say appeared to live up to Pyongyang's claim that the device that was exploded was a hydrogen bomb, exponentially more powerful than a normal atomic device.
That test, combined with the rapid pace of missile launches and North Korea's stated goal of wanting to be able to strike the mainland United States with a nuclear-tipped missile, has caused alarm around the world.
The UN Security Council imposed its toughest-ever sanctions against North Korea on Tuesday, setting limits on North Korea's oil imports and banning its textile exports.
But the new sanctions were a compromise. The US had to tone down its demands, which included a total oil embargo and a global travel ban on leader Kim Jong Un, in order to win the support of China and Russia.
Tillerson's statement reflected the Trump Administration's frustration with the reluctance of Beijing and Moscow to inflict real pain on Pyongyang. The North Korean statement that hit out at Japan also, meanwhile, reflected Pyongyang's anger at what it called the "heinous sanctions resolution". The North Korean people and military wanted "the Yankees, chief culprit in cooking up the 'sanctions resolution', [to] be beaten to death as a stick is fit for a rabid dog," the statement said.
The Japanese Government estimates that the force of the September 3 nuclear test was 160 kilotons - more than 10 times the size of the bomb dropped on Hiroshima - but some analysts have said its yield could have been as much as 250 kilotons.
US Defence Secretary Jim Mattis, travelling from Washington to view US nuclear weapons at Minot Air Force Base, North Dakota, said on Thursday that the North Korean nuclear test appeared to be "100 kilotons or more".
"It's a large one," he said.
Earlier, Air Force General John Hyten, the chief of US Strategic Command, said that he "had to assume" that North Korea had probably tested a hydrogen bomb, based on the size of the explosion.
Speaking just before the missile was launched, Hyten, who oversees US nuclear forces and monitors North Korea, told reporters that the size, yield and other indications seen in North Korea's most recent nuclear test "equates to a hydrogen bomb". He said the test was significant "because of the sheer destruction and damage you can use and create with a weapon of that size".
"The change from the original atomic bomb to the hydrogen [bomb] changed our entire deterrent relationship with the Soviet Union," Hyten said. "It is significantly of concern not just to Strategic Command but to everybody in the free world."
