According to Seoul's Joint Chiefs of Staff office, seismic waves measuring magnitude 5.7 were detected from Punggye-ri, North Hamgyong Province in northeastern region of North Korea at 12:29 p.m. Punggye-ri is the site of Pyongyang's previous nuclear tests.
It marks North Korea's sixth nuclear test ever.
"We will convene a National Security council meeting to gather and analyze the information", Abe said in a live television broadcast prior to Kono's announcement.
North Korea said Sunday it has successfully produced a hydrogen bomb to be loaded on a newly-developed intercontinental ballistic missile, amid growing fears over its rapid progress in upgrading its weapons and the possibility of another nuclear test.
Beijing's response was predictable - condemnation, urging an end to provocation and dialogue.
Those readings would put the size of the explosion at several times larger than previous North Korean tests.
"But they won't go far enough to have an impact on North Korea's determination to become a nuclear power", the diplomat said, speaking on condition of anonymity.
A hydrogen bomb, or fusion bomb, is far more powerful than atomic bombs, or fission bombs, that the country has already tested.
Under that proposal, North Korea would suspend nuclear and missile tests in exchange for the US and South Korea suspending their joint military exercises, CNN reported.
August 3, 2016: North Korea fires a ballistic missile directly into Japan's maritime economic zone for the first time.
North Korea is thought to have a growing arsenal of nuclear bombs and has spent decades trying to flawless a multistage, long-range missile to eventually carry smaller versions of those bombs.
"We can not deny it was an H-bomb test", Onodera said.
July 8, 2016: US and South Korea announce plans to deploy an advanced missile defence system - THAAD (Terminal High Altitude Area Defense).
April 5, 2009: Launches long-range rocket which flies over Japan and lands in the Pacific, in what it says is an attempt to put a satellite into orbit.
The North said in its statement Sunday that its H-bomb "is a multi-functional thermonuclear nuke with great destructive power which can be detonated even at high altitudes for super-powerful EMP (electromagnetic pulse) attack according to strategic goals".
And the head of the UN's nuclear watchdog, IAEA director general Yukiya Amano was the test was an "extremely regrettable act" that was "in complete disregard of the repeated demands of the global community".
Dictator Kim Jong-un personally inspected the loading of the H-bomb onto the ICBM during a visit to the North's Nuclear Weapons Institute, Pyongyang's state media said Sunday.
But as NPR's Elise Hu reported, Jenny Town, the assistant director of the U.S. -Korea Institute at John Hopkins' School of Advanced International Studies says a policy of increasing pressure is misconstrued as "hostility", which, Town argues, "justifies its need for nuclear weapons".
March 7, 2017: United States begins deploying THAAD missile defence system in South Korea.