A small earthquake that occurred early on Saturday near North Korea's known nuclear test site was likely a natural quake, South Korea's weather agency said, Reuters reported.

A 2.5-magnitude quake shook an area just northeast of North Korea's Punggye-ri nuclear test site at 2:54am local time, the Korea Meteorological Administration of South Korea said.

"It is assessed to be a natural earthquake," the agency said in an advisory. It gave the depth of the tremor at 23 kilometers.

The area is the location of small quakes earlier in the year which analysts said were because of geological instability stemming from activities at the test site.