China's earthquake administration said in statement that the earthquake occurred Saturday at around 0830 UTC and was recorded at a depth of zero kilometers.

A number of previous shallow quakes in North Korea, including the most recent earlier this month, have turned out to be caused by the rogue state's nuclear tests, China's official Xinhua news agency reported.

According to South Korea's meteorological agency, a 3.0-magnitude earthquake was detected around Kilju in North Hamgyong Province, where North Korea's Punggyeri nuclear site is located. However, the agency said its initial assessment suggested the tremor was natural.

"We use several methods to tell whether earthquakes are natural or manmade," an official at the agency told the Reuters news agency on condition of anonymity. "A key method is to look at the seismic waves or seismic acoustic waves and the latter can be detected in the case of a manmade earthquake. In this case we saw none. So as of now we are categorizing this as a natural earthquake."

Chinese seismologists said they believed the tremor was caused by an explosion. 

Lassina Zerbo, the executive secretary of nuclear proliferation watchdog CTBTO, said on Twitter that analysts were investigating the "unusual seismic activity," about 50 kilometers (31 miles) from the site of previous tests.

Pyongyang conducted its sixth and most powerful nuclear test on September 3, claiming it had tested a hydrogen bomb that can be loaded onto an intercontinental ballistic missile (ICBM). All of its tests have resulted in earthquakes of magnitude 4.3 or above.

The regime's nuclear activities have led to rising tensions on the Korean peninsula, and more recently have resulted in verbal clashes between US President Donald Trump and North Korean leader Kim Jong Un.

Trump called Kim a "madman" on Friday, a day after the North Korean leader dubbed him a "mentally deranged US dotard" who would face the "highest level of hard-line countermeasure in history."

nm/jlw (Reuters, AFP, AP, dpa)