The White House said it is aware of seismic activity near North Korea's nuclear site as the communist nation is strongly suspected of conducting what would be its fifth nuclear test.

"We are aware of seismic activity on the Korean Peninsula in the vicinity of a known North Korean nuclear test site. We are monitoring and continuing to assess the situation in close coordination with our regional partners," National Security Council spokesman Ned Price said.

He did not provide further details.

South Korea said a magnitude 5 artificial earthquake struck near North Korea's Punggye-ri nuclear test site, strongly suggesting the possibility of a nuclear test.

If confirmed, it would be the North's fifth nuclear test. The four previous tests came in 2006, 2009, 2013 and in January this year. (Yonhap)