An earthquake that appears to have been man-made near a known nuclear testing site in North Korea was detected by several monitoring agencies on Wednesday.

The United States Geological Service reported a 5.1 magnitude quake that South Korea said was 49 kms (30 miles) from the Punggye-ri site where the North has conducted nuclear tests in the past.

"We suspect a man-made earthquake and are analyzing the scale and epicenter of the quake with the geoscience and mineral resource institute of South Korea," a Korea Meteorological Administration official told Reuters by phone.