A strong shallow earthquake struck the Democratic People's Republic of Korea (DPRK) on Sunday, triggering suspicions that it might be caused by explosion.

In its latest update, the U.S. Geological Survey reported that the tremor happened at 0330 GMT and measured 6.3 magnitude, with an epicenter 24 km east-northeast of Sungjibaegam and zero km deep.

The institution noted that it might be caused by explosion and that its epicenter was located near the site where the DPRK detonated nuclear explosions in the past.

The China Earthquake Networks Center also placed the magnitude at 6.3 and the depth of its epicenter at zero km, and noted that explosion was suspected.

In the wake of the earthquake, South Korean President Moon Jae-in called an emergency meeting of the National Security Council.

A second quake of 4.6 magnitude later followed, about an hour after the first artificial tremor was detected near the DPRK's main nuclear test site, South Korea's Yonhap news agency reported Sunday.