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.
China's Commerce Ministry said in a statement late on Friday that restrictions on refined petroleum products would apply from Oct 1, and on liquefied natural gas immediately.
After a week in which, with tweets and in a speech before the United Nations General Assembly, Trump introduced the derogatory nickname "Rocket Man" for Kim into worldwide news coverage and left open his prerogative to "totally destroy" North Korea, the president gave no ground on Friday in his public standoff with his adversary.
He said the agency's analysts were "looking at unusual seismic activity of a much smaller magnitude" in North Korea.
Pyongyang says it will not give up on its nuclear deterrence unless Washington ends its hostile policy toward the country and dissolves the US-led United Nations command in South Korea.
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".
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. "So as of now, we are categorising this as a natural quake".
An official of South Korea's Meteorological Agency said acoustic waves should be detected in the event of a man-made natural disaster.
A USA intelligence official and US -based non-governmental experts said their initial assessment was that the quake was either natural or connected to North Korea's latest and largest nuclear test on Sept.3, and not caused by a new nuclear test.
CTBTO Executive Secretary Lassina Zerbo tweeted seismographic graphs from Saturday's quake alongside those from the second quake on September 3, with both data patterns looking broadly similar.
All of North Korea's six nuclear tests registered as earthquakes of magnitude 4.3 or above. Analysis is ongoing, he said in a Twitter message.
He called out the leader of the North Korean communist regime, Kim Jong-Un, stating that by making nuclear threats against the United States and its allies, "Rocket Man is on a suicide mission for himself and for his regime".
There was no immediate reaction from China's Foreign Ministry. On Thursday, the USA unveiled its own set of economic sanctions targeting North Korea.
Donald Trump later used his speech to the UN General Assembly to tell the world he would "totally destroy" North Korea if the United States of America was threatened by its regime.
Atmospheric tests of nuclear-armed missiles, as NPR's Geoff Brumfiel reported, are risky for a host for reasons, including the potential for sending nuclear fallout in unpredictable patterns and, if a test were to be administered by North Korea, in the direction of the U.S.
"This doesn't in any way, of course, justify the DPRK's missile and nuclear program, but to ignore the reasons for them is to be very short-sighted", Nebenzia said, using the initials of North Korea's official name, the Democratic People's Republic of Korea.