South Korea says North Korea may have conducted a sixth nuclear test, Yonhap reports citing Blue House.
The United States Geological Survey said a tremor that's 6.3 in magnitude struck North Korea on Sunday.
Previous recent tremors in North Korea have been caused by nuclear tests.
Yonhap says the quake took place in Kilju county where its nuclear test site Punggye-Ri is located.
South Korea has convened a national security council meeting to discuss the quake.
The tremor is only 10km deep, the USGS said.