A 5.1 magnitude earthquake has been detected in North Korea, close to a site previously used for nuclear tests.
Chinese and South Korea officials said there were indications the tremor was man-made, meaning the North may have carried out a new nuclear test.
South Korean ministers are holding an emergency meeting, state media said.
North Korea is believed to have conducted three underground nuclear tests since 2006, all at a site called Punggye-ri.
The new tremor was detected about 50km (30 miles) from Punggye-ri at a depth of about 10km, according to the US Geological survey. (BBC)