A magnitude 5 earthquake was detected near North Korea's nuclear site in its northeastern region on Friday, the South Korean military said, raising speculation that the North conducted a nuclear test.

"An artificial quake was detected near North Korea's Punggye-ri at around 9:30 a.m.," South Korea's Joint Chiefs of Staff said, adding that it is analyzing whether the country carried out a nuclear test.

A government source said there is a high possibility that Pyongyang conducted a nuclear test on the occasion of its 68th anniversary of the establishment of its regime.

"Given the location and magnitude of the seismic activity detected, the quake is likely to have been caused by a nuclear device," the source said.

The epicenter is believed to be the same as the location where North Korea conducted its fourth nuclear test in January. Pyongyang also conducted nuke tests in 2006, 2009 and 2013.

In March, the UN Security Council slapped its toughest sanctions on Pyongyang for its nuclear test and long-range rocket launch early this year.

North Korea has threatened to conduct a fifth nuclear test, claiming that it has the full capacity to carry out pre-emptive nuclear strikes.

In March, North Korean leader Kim Jong-un ordered his officials to conduct a nuclear warhead test and more test-fires of ballistic missiles as soon as possible.

South Korea's prime minister plans to hold an emergency National Security Council meeting later in the day to discuss how to deal with the latest development.

Seoul's foreign ministry said that it is discussing the issue with the US and other countries via diplomatic channels. (Yonhap)