Reports have suggested that Pyongyang could soon carry out a sixth nuclear test, but the respected 38 North website said last week that satellite imagery of the Punggye-ri test site showed no evidence that a blast was imminent.
The depth of the quake was recorded as zero meters, the China natural disaster administration said, according to Reuters.
Melissa Hanham of the Middlebury Institute for International Studies in California said the latest images released by the North could not be proved real of themselves.
Her comments came before the state-run KCNA news agency reported that Pyongyang had developed a more advanced nuclear weapon and that Kim had inspected a hydrogen bomb that could be loaded onto a new intercontinental ballistic missile.
To back up its claims to nuclear mastery, such tests are vital. The United States Geological Survey called the quake a "possible explosion".
Sunday's development comes amid heightened tensions after North Korea tested two ICBMs in July.
Trump and South Korean President Moon Jae-in said on Saturday they plan to revise a 43-year-old joint treaty that caps the number and range of South's ballistic missiles.
Russian Federation warns U.S. against using force over North Korea
On August 29, North Korea test-fired another missile. Posted: Sep. 1, 2017 7:00 am Updated: Sep. Petersburg, Yekaterinburg and Vladivostok.
"Though we cannot verify the claim, [North Korea] wants us to believe that it can launch a thermonuclear strike now, if it is attacked", Adam Mount, a senior fellow at the Center for American Progress, told Reuters news agency.
North Korea further raised regional tensions on Tuesday by launching an intermediate-range ballistic missile over Japan, drawing global condemnation.
Pyongyang's assertion that "this warhead is variable-yield and capable of specialized weapons effects implies a complex nuclear strategy", Mount added.
The White House said that President Donald Trump spoke with Prime Minister Shinzo Abe of Japan regarding "ongoing efforts to maximize pressure on North Korea".
Questions remain over whether Pyongyang has miniaturized its weapons and whether it has a working hydrogen bomb. The first involved what it claims to have been a hydrogen bomb and the second was its most powerful ever.
Aside from the factuality of the North's claim, the language in its statement seems a strong signal that Pyongyang will soon conduct its sixth nuclear weapon test, which is crucial if North Korean scientists are to fulfill the national goal of an arsenal of viable nuclear ICBMs that can reach the US mainland.