He said New Zealand would join the worldwide community in considering what measures can be taken.
State-controlled media say it was a hydrogen bomb. North Korea claimed it achieved that milestone after a nuclear test past year.
North Korean leader Kim Jong-Un approves a document of the country's first ICBM test launch.
Last September, North Korea conducted its fifth nuclear test, showing its determination to be a nuclear-armed country despite ever tougher sanctions.
The provocation came amid heightened tensions after North Korea tested two ICBMs in July.
The North has repeatedly claimed that it has a thermonuclear weapon, which can be far more powerful than other nuclear devices. That would be 3:30 p.m.in Seoul and Tokyo, and 2:30 a.m. EDT.
The report states that Kim inspected a hydrogen bomb that will be loaded on a new intercontinental ballistic missile "with great destructive power". However, the said picture couldn't be verified independently and no journalists were present when the photo was taken. The Korea Meteorological Administration estimated that the nuclear blast yield Sunday was between 50 to 60 kilotons. NORTH Korea has confirmed it has tested a thermonuclear bomb with "complete success".
South Korea's military says North Korea is believed to have conducted its sixth nuclear test.
The second quake measured 4.6.
China's Caixin manufacturing PMI hits six-month high
New contracts predominately came from the domestic market, although exports remained strong, if down on July's near-record high. Manufacturers' selling prices rose at a solid, yet slower, pace.
This would be North Korea's sixth nuclear test, and the first since President Trump was inaugurated.
United States Geological Survey recorded the magnitude at 6.3 - larger than any previous test.
Kim's regime has produced a miniaturized nuclear warhead that can fit atop its missiles, surpassing a key technological hurdle, the Washington Post reported August 8, citing an Defense Intelligence Agency analysis completed in July.
South Korea, the United States, and Japan have been unnerved by the North's weapons programs, which Pyongyang has been defiantly advancing as countermeasures to their hostility. Its military said it has strengthened its monitoring and readiness while considering a variety of possible responses in collaboration with the US.
In January 2016, North Korea conducted its fourth nuclear test, which Pyongyang claimed to be a test of a hydrogen bomb.
The seismic data resembled that of a 6.3 magnitude quake, suggesting that North Korea tested a nuclear device with an explosive yield of at least 100 kilotons, much larger than any of the North's previous tests.
He earlier said that North Korea would be crossing a "red line" if it weaponises a nuclear-tipped ICBM.
Despite the worldwide pressure, however, missile and nuclear tests have continued unabated. That test was one of two tests conducted a year ago.
An earlier report by KCTV claimed the bomb was small enough to fit on an intercontinental ballistic missile.
South Korea and Japan are gathering and analysing data to confirm details of the test, which Japanese Prime Minister Shinzo Abe said could not be tolerated.