The epicentre is roughly the same as that of a previous shallow earthquake on September 3, which turned out to be caused by a North Korean nuclear test, the official Xinhua news agency said.
The earthquake comes after days of increasingly bellicose rhetoric between US President Donald Trump and North Korean leader Kim Jong-Un's regime over Pyongyang's nuclear ambitions that has raised international alarm.
The nuclear proliferation watchdog CTBTO said unusual seismic activity detected in North Korea on Saturday took place around 50 km (31 miles) from previous tests.
"Korean Peninsula unusual #seismic activity: LAT=41.36 LON=129.76 mb=3.5 About 50 km from prior tests. #CTBT Analysts investigating," CTBTO Executive Secretary Lassina Zerbo said in a Twitter post.
There seemed to be some initial difference of opinion, however, with Seoul's Korea Meteorological Agency (KMA) saying that it had registered a tremor of a similar size, but judged it a "natural quake".
The quake comes amid soaring tensions over Pyongyang's weapons programme, with the firing of two missiles over Japan in recent weeks and its sixth and largest nuclear test earlier this month.
The September 3rd test was North Korea's most powerful detonation, triggering a much stronger 6.3-magnitude quake that was felt across the border in China.
This week marked a new level of acromony in a blistering war of words between Kim and Trump, with the North Korean leader calling the American president "mentally deranged" and a "dotard".
Trump has dubbed Kim a "madman" and sought to ratchet up sanctions against the isolted regime, which says it needs nuclear weapons to protect itself against the threat of invasion.
Pyongyang later said it had tested a hydrogen bomb that could be fitted onto a missile -- an assertion that no foreign government has so far confirmed.
The move prompted global condemnation, leading the UN Security Council to unanimously adopt new sanctions that include restrictions on oil shipments.
Hydrogen bombs, or H-bombs, are thermonuclear weapons far more powerful than ordinary fission-based atomic bombs, and use a nuclear blast to generate the intense temperatures required for fusion to take place.
Kim on Friday threatened the "highest level of hard-line countermeasure in history" in a tirade against Trump's warning that Washington would "totally destroy" the North if the US or its allies were threatened.
Monitoring groups estimate that the nuclear test conducted in North Korea earlier this month had a yield of 250 kilotons, which is 16 times the size of the US bomb that destroyed Hiroshima in 1945.
Washington announced tougher restrictions Friday aimed at curbing North Korea's nuclear and ballistic missile programme, building on new tough United Nations sanctions aimed to choke Pyongyang of cash.
Russia and China have both appealed for an end to the escalating rhetoric between Washington and Pyongyang.
But on the fringes of the UN meeting this week, North Korean Foreign Minister Ri Yong-ho upped the tensions further, telling reporters Pyongyang might now consider detonating a hydrogen bomb outside its territory.
