North Korea conducted its fifth nuclear test on Friday, South Korean President Park Geun Hye said, with the atomic explosion coming on the anniversary of the nation's founding.
Park said she strongly condemned the latest provocation from Kim Jong Un's isolated regime -- calling it an action of "maniacal recklessness" -- and warned its actions would lead to its self-destruction. South Korea will increase pressure on Pyongyang to give up its nuclear arms, she said in a statement on the presidential office website.
South Korean officials said the blast set off an artificial earthquake that was detected around 9:30am Seoul time, with the defense ministry citing an explosion of 10 kilotons. The United States Geological Survey put the quake magnitude at 5.3.
A tremor of 5.1 in a similar location was recorded before North Korea's fourth nuclear test in January, a blast that was estimated around six kilotons.
Chief Cabinet Secretary Yoshihide Suga said North Korea's arms development was a threat to Japan and the country would consider further sanctions against the regime.
The test comes a day after U.S. President Barack Obama left Asia following his swansong trip as leader. His visit took in a clutch of global summits in China -- where he attended a G-20 meeting hosted by President Xi Jinping -- and Laos. During those meetings he and leaders from countries such as Japan and South Korea urged stronger action to curb Kim's nuclear ambitions. Park said Friday she had spoken with Obama about the nuclear test.
"North Korea has prepared everything to conduct a nuclear test any time and has just been waiting for the right timing," said Lim Eul Chul, a professor of international political economy at Kyungnam University in Seoul.
North Korea has been seeking more miniaturized capability, Lim said. "The smaller the warhead, the further the weapon can fly. The results would have to come out, but for now I see that North Korea's nuclear technology has come to a stage where it's right before being arranged for combat."
The Kospi Index declined in Seoul, falling 1.4 percent as of 12:25 p.m. local time to head for the steepest daily drop among Asian stock gauges. The won weakened 0.7 percent after an earlier fall of as much as 1 percent. The yen strengthened 0.4 percent against the dollar, extending its weekly advance to 1.8 percent.
"We can probably say that the market is reacting a little to signs North Korea conducted a nuclear test," said Soichiro Monji, general manager for the economic research department at Daiwa SB Investments Ltd. "We're not seeing a huge amount of trading on this news, but it does contribute to a slight risk-off mood. The yen is strengthening, and shares aren't managing to rise."
North Korea test-fired a trio of ballistic missiles that landed within a few hundred kilometers of Japan's coast earlier this week. The regime, which has repeatedly flouted United Nations Security Council resolutions barring its ballistic missile activities, has conducted at least 22 launches this year, according to U.S. officials.
China has done more on sanctions against North Korea than previous rounds of penalties but could still "tighten up" in prodding Kim's regime, Obama told reporters on Thursday in Laos. Obama said he had told Xi that China needs to "work with us more effectively" to rein Kim in.
Tensions in North Asia have also been running high over a plan to deploy a U.S. missile defense system known as Thaad in South Korea. The Chinese have protested that move, which U.S. officials insist is only intended to protect South Korea. Russia has also objected.
The latest blast probably reflects North Korean efforts to cause further fractures between the U.S. and China over Thaad, said Lee Woo Young, a professor at the University of North Korean Studies in Seoul. "The test would show North Korea's willingness to break the power balance in the East Asia region."
Obama said he noted Xi's objection to Thaad and that the U.S. is not looking for a diplomatic tussle over the missile shield. Still, he said, "we cannot have a situation where we're unable to defend ourselves or our treaty allies against increasingly provocative behavior."
"They need to work with us more effectively to change Pyongyang's behavior," Obama said, referring to China.
The big question for the international community is whether it can match its condemnation of North Korea with action, according to Scott Snyder, a senior fellow for Korea studies at the Council on Foreign Relations.
"A second question is whether the United States and China can set aside strategic mistrust sufficiently to coordinate a set of actions that would make clear that Kim Jong Un's current path is unacceptable and force him to turn around and accept denuclearization."