South Korea operates 24 nuclear reactors, majority on it's east coast facing Japan, according to the World Nuclear Association.

For North Korea's actions have been clearly telegraphed.

US President Donald Trump said North Korea had signaled its "contempt for its neighbors" and that "all options are on the table" in terms of a US response.

The Korean Central News Agency said the launch was a "muscle-flexing" countermeasure to the Ulchi Freedom Guardian joint exercises that conclude on Thursday. "The US has been talking to North Korea, and paying them extortion money, for 25 years".

The report cited the USGS as saying the first tremor occurred at around 12 noon North Korea time.

The piece also framed the test as a show of force in response to the annual Ulchi-Freedom Guardian joint military drills being conducted by the US and South Korean militaries.

The United States has repeatedly urged China, the North's sole major ally, to do more to rein in its neighbour. But they went ahead as planned.

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But the Institute for Science and International Security, a USA non-profit dedicated to providing public knowledge of nuclear proliferation and international security, tweeted that North Korea can "build any H bomb (two stage) model it wants and call it whatever it wants but that does not make it real".

"We don't know if this thing is full of styrofoam, but yes, it is shaped like it has two devices", she said on Twitter. "And now it's just happening".

Kim Jong Un, who visited the country's nuclear weapons institute, "watched an H-bomb to be loaded into new ICBM" and "set forth tasks to be fulfilled in the research into nukes", KCNA said. On July 4, he made good on this.

Tokyo said there was no reported damage from the missile. "This reckless act of launching a missile that flies over our country is an unprecedented, serious and important threat".

North Korea is doing several things with these launches, analysts say. Such practices are one reason why North Korea is considered a human rights pariah nation where crimes against humanity are state policy.

"This was an operational test", said Vipin Narang, an expert on nuclear proliferation and strategy at the Massachusetts Institute of Technology, noting that this launch took place at a new site, just north of the capital.

"He does value his own life", Abrahms said.

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Guam is 3,400 kilometers (2,110 miles) away from North Korea, but South Korea's military said the North may have fired the missile at a shorter range. The missile had a full range of 4990km, the ministry said.

The state news report arrives as the US and North Korea remain entangled in nuclear brinksmanship.

"We passed the point of trying to resolve North Korean nuclear problem through dialogue", Koh said.

Third, the launch can come as a refutation of President Trump's claims that Pyongyang has been frightened by his threats of "fury and fire". "It's a whack-a-mole problem".

Previous sanctions have had little effect, however, and the impoverished nation has continued with its nuclear weapons and ballistic missile programs regardless.

South Korea's Joint Chiefs of Staff reported a magnitude 5.6 quake.

Even as his officials try to find an opening for negotiations, Trump on Wednesday (Thursday NZT) ruled out diplomacy. "Talking is not the answer!" Leaders around the world should put themselves in the shoes of Japanese, Thai and North and South Korean families who still wonder, after decades, what has happened to their loved ones who remain disappeared without a trace.

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