Kyodo News of Japan reported: "The Japanese government said there is a possibility that the seismic event was caused by a nuclear test and that it is gathering and analyzing information."

South Korea has called it an 'artificial quake'.

"Considering the waveform and the amplitude of the earthquake, it seems certain that it was an artificial quake," a  South Korean meteorological administration official was quoted as saying by Yonhap News Agency.

"(We are) going through a thorough analysis based on the high possibility of it being a nuke test," the official said.

According to USGS website, an earthquake measuring 5.1 on the Richter Scale hit North Korea with the epicentre being 19kms east-north-east of North Korea's Sungjibaegam town.