Kirk Spitzer

USA TODAY

TOKYO — North Korea announced Wednesday that it tested its first hydrogen bomb, a major leap in its nuclear program that promptly drew international condemnation.

A statement by the secretive state’s government said “the first H-bomb test was successfully conducted” at 10 a.m. local time Wednesday.

The statement, carried by the official Korean Central News Agency, said the nation has “proudly joined the advanced ranks of nuclear weapons states" and is "equipped with the most powerful nuclear deterrent.”

The announcement came soon after a magnitude-5.1 earthquake was reported by the U.S. Geological Service 30.4 miles from the city of Kilju, North Korea, where the country's Punggye-ri nuclear test site is located.

That is the same area where North Korea conducted nuclear tests in 2006, 2009 and 2013.

The USGS put the depth of the earthquake at 6 miles below the surface, but the South Korea's geological agency said it was near the surface. The earthquake was detected just after 10 a.m. Tokyo time (8 p.m. ET).

A hydrogen bomb is generally considered to be more powerful than a typical nuclear explosive. Also called a thermonuclear bomb, it uses fusion in a chain reaction to create a more powerful detonation than a typical atomic bomb, which uses fission. A hydrogen bomb uses an atomic bomb inside its core to set off fusion reactions that have a devastating effect.

Kim Jong Un says he's ready for war in New Year speech

South Korea's presidential office convened an emergency security meeting Wednesday morning.

South Korean President Park Geun-hye called for a swift, accurate analysis of the North’s claim at the start of the meeting.

“It’s not only grave provocation of our national security, but also an act that threatens our lives and future. It’s also a direct challenge to world peace and stability,” she said.

She said the South will sternly deal with any additional provocation by the North, and ordered the military to maintain readiness in cooperation with U.S. troops.

The U.N. Security Council is planning to hold an emergency meeting on the reported test later.

A television anchor in North Korea said in a propaganda-heavy statement that the North tested a miniaturized hydrogen bomb, elevating the country's nuclear prowess "to the next level" and providing it with a weapon against the U.S. and others. The TV anchor said the test went off perfectly.

A large crowd celebrated in front of Pyongyang’s main train station as the announcement was broadcast on a big screen.

North Korean university student Ri Sol Yong, 22, said: “If we didn’t have powerful nuclear weapons, we would already have been turned into the slaves of the U.S.”

The Obama administration has been "re-balancing" U.S. forces to the Asia-Pacific region in part to deal with North Korea's nuclear weapons and ballistic missile programs.

World reacts to N. Korea's hydrogen bomb test claim

The White House said after the earthquake that it was aware of the seismic activity and of North Korea's claims of a nuclear test.

"While we cannot confirm these claims at this time, we condemn any violation of U.N. Security Council resolutions and again call on North Korea to abide by its international obligations and commitments," said Ned Price, the spokesman for the National Security Council. "We have consistently made clear that we will not accept it as a nuclear state. We will continue to protect and defend our allies in the region, including the Republic of Korea, and will respond appropriately to any and all North Korean provocations."

U.S. Ambassador Caroline Kennedy met with Japan’s Foreign Minister Fumio Kishida on Wednesday to discuss the test.

“We condemn any violation of the U.N. Security Council resolutions and call again on North Korea to abide by its international obligations and commitments,” Kennedy said. “We stand with Japan and our other allies in solidarity against North Korean provocations, and we will work closely with them in the coming days.”

Kishida said Japan would seek a new UN resolution condemning the test.

North Korean leader Kim Jong Un said in an annual New Year's speech last week that the country was ready for war if provoked by "invasive" outsiders, but did not repeat past threats to use the country's nuclear weapons or long-range missiles.

A confirmed test would mark another big step toward Pyongyang's goal of building a warhead that can be mounted on a missile capable of reaching the U.S. mainland.

The test drew immediate reaction from North Korea’s neighbors.

Japan Prime Minister Shinzo Abe said the test represents a threat to Japanese security and is “totally intolerable,” according to Kyodo News Service.

Abe said Japan “strongly condemns” the test and would have a “firm response.”

China, North Korea’s main ally, said it “firmly opposes” the test.

British Foreign Secretary Philip Hammond, who is currently visiting China, condemned the action and said he and his Chinese counterpart Yang Jiechi agreed to work with other members of the U.N. Security Council toward “a robust international response.”

Lee Cheol Woo, a South Korean lawmaker, said the country’s spy agency told him in a private briefing that the North may not have conducted a hydrogen bomb test because the estimated explosive yield of six kilotons and magnitude 4.8 quake detected Wednesday were a fraction of the hundreds of kilotons of explosive yield that a typical successful hydrogen bomb test would have.

He said an estimated explosive yield of 7.9 kilotons and a magnitude 4.9 quake were reported after the 2013 nuclear test.

Robert Kelly, associate professor of political science and diplomacy at Pusan National University, in South Korea, said he is not convinced that the test represents a hydrogen bomb and said the footprint more closely resembles that of the 2013 atomic bomb test.

“Hydrogen bombs are an order of magnitude more powerful in the amount of energy they release. They are fusion weapons... it would be a major upgrade if they managed to pull it off,” he said.

He added: “North Korea makes all sorts of claims and there is no reason, given their history of lying and dissembling, to take them at their word. I am waiting for definitive word from the South Korean and or American governments.”

North Korea is believed to have three types of operational ballistic missiles, with a maximum range of 800 miles. That’s enough range to hit targets in South Korea and Japan, including the massive U.S. military bases in both countries.

The North also is believed to be working on two types of long-range missiles that could hit targets in the U.S. territory of Guam, and in Alaska and Hawaii.

Pyongyang is thought to have a handful of crude nuclear weapons. The United States and its allies worry about North Korean nuclear tests because each new blast brings the country closer to perfecting its nuclear arsenal.

Contributing: The Associated Press