http://www.bbc.com/news/world-asia-41139445
https://www.washingtonpost.com/world/north-korea-apparently-conducts-another-nuclear-test-south-korea-says/2017/09/03/7bce3ff6-905b-11e7-8df5-c2e5cf46c1e2_story.html?deferJs=true&hpid=hp_no-name_no-name%3Apage%2Fbreaking-news-bar&outputType=default-article&tid=a_breakingnews&utm_term=.c9c27199d5bf
Edit: I changed the 2nd link to the Washington Post as the NYTimes link hadn't updated the magnitude of the tremor and I didn't want to post conflicting info.
US seismologists said the 6.3 magnitude quake in the north-east of the country was a "possible explosion".
South Korea immediately convened a national security council meeting.
The tremor comes hours after North Korean leader Kim Jong-un was pictured with what state media said was a new type of hydrogen bomb.
State media said the device could be loaded on to a ballistic missile. Neither claim could be independently verified.
South Korea officials said the quake took place in Kilju County, where the North's Punggye-ri nuclear test site is situated.
China's Earthquake Administration described the tremor as a "suspected explosion".
Initial reports from the US Geological Survey put the tremor at 5.6 magnitude with a depth of 10km (six miles) but this was later changed to 6.3 magnitude at 0km.
North Korea carried out its last nuclear test in September last year. It has defied UN sanctions and international pressure to develop nuclear weapons and to test missiles which could potentially reach the mainland US.
A series of recent missile tests has caused growing international unease.
In a report on Sunday, the North's state news agency KCNA said Kim Jong-un had visited scientists at the nuclear weapons institute and "guided the work for nuclear weaponisation".
https://www.washingtonpost.com/world/north-korea-apparently-conducts-another-nuclear-test-south-korea-says/2017/09/03/7bce3ff6-905b-11e7-8df5-c2e5cf46c1e2_story.html?deferJs=true&hpid=hp_no-name_no-name%3Apage%2Fbreaking-news-bar&outputType=default-article&tid=a_breakingnews&utm_term=.c9c27199d5bf
North Korea appears to have conducted another nuclear test, the South Korean government said Sunday after seismic authorities detected an artificial earthquake near Pyongyang regime's known nuclear test site.
This would be North Korea's sixth nuclear test, and the first since President Trump was inaugurated. The action probably will increase already high tensions between the Trump administration and Kim Jong Un's regime.
The U.S Geological Survey said it had recorded a 6.3 magnitude earthquake exactly at noon Sunday local time, near North Korea's known nuclear test site in the country's northeast region. North Korea's recent nuclear tests have also happened exactly on the hour.
Edit: I changed the 2nd link to the Washington Post as the NYTimes link hadn't updated the magnitude of the tremor and I didn't want to post conflicting info.