North Korea, which carries out its nuclear and missile programs in defiance of United Nations Security Council resolutions and sanctions, said on state television that a hydrogen bomb test ordered by leader Kim Jong Un had been a "perfect success".
In a surprise announcement on state TV, North Korea said it had tested a powerful hydrogen bomb that can be loaded on to an intercontinental ballistic missile, in a move that is expected to increase pressure on Trump to defuse the growing nuclear crisis on the Korean peninsula.
Early Sunday on Twitter, Trump called North Korea "a rogue nation which has become a great threat and embarrassment to China".
As North Korea's most important trading partner, the position of China - a permanent member of the U.N. Security Council - will be closely watched.
"President Trump and President Moon pledged to continue to apply strong diplomatic and economic pressure on North Korea and to make all necessary preparations to deter and defend against the growing threat posed by North Korea", read a White House statement. What he called South Korea's "talk of appeasement" would not work as "they (the North Koreans) only understand one thing!"
"We have no choice but to judge that (the test) was a success", Onodera said.
"I was eating brunch just over the border here in Yanji when we felt the whole building shake", Michael Spavor, director of the Paektu Cultural Exchange, which promotes business and cultural ties with North Korea.
North Korean leader Kim Jong Un.
Renmin University's professor of worldwide relations, Shi Yinhong, had warned earlier in the week that China was in a hard diplomatic situation - North Korea was acting increasingly hatefully towards China as it toughened economic sanctions.
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However, this does appears to be the biggest and most successful nuclear test by North Korea to date - and the messaging is clear.
Experts say it is almost impossible to verify with certainty North Korea's claim that it detonated a hydrogen bomb, which is also known as a thermonuclear weapon, or whether it can actually be used successfully on a missile.
But Suga stressed that the risk of radioactive material being released into the air from underground nuclear tests is "generally low".
She was seen crying or holding back tears on both occasions, a departure from the thunderous tone she is best known for outside North Korea. They use fusion - the merging of atoms - to unleash huge amounts of energy, whereas atomic bombs use nuclear fission, or the splitting of atoms.
However many analysts believe that even a limited military strike on North Korea could be potentially catastrophic. Shinzo Abe, the prime minister of Japan, called the nuclear test "absolutely unacceptable", and immediately deployed planes to detect radiation in the atmosphere.
Suga said imposing restrictions on the North's trade in crude oil and oil products is "one of the options" Japan might seek.
Beijing's response was predictable - condemnation, urging an end to provocation and dialogue.
Russian President Vladimir Putin, who is now in China for a summit of BRICS leaders, discussed the bomb test with Chinese President Xi Jinping earlier on Sunday.
Even the state-controlled media will find it hard to ignore the fact that their man has been upstaged - embarrassed too - by its nearly universally ostracised ally and neighbour.