President Obama says the United States "does not and never will" accept them as a nuclear state.
In a statement released Friday, Obama called the test "a great threat to regional security." He said North Korea's actions would have "serious consequences."
The alleged test of the nuclear device (it has not been confirmed by outside sources) comes just days after North Korea also fired three medium-range ballistic missiles in the direction of Japan.
Leaders in the reclusive Stalinist nation claim the nuclear device was small and light enough to be used as a missile warhead.
BREAKING: North Korea says it has conducted a "nuclear warhead explosion" test meant to counter what Pyongyang calls U.S. hostility.— The Associated Press (@AP) September 9, 2016
North Korea says its latest nuke test was a success, taking its bomb program to a new level.
BREAKING: China says it "resolutely opposes" N. Korea's nuke test, "intensely urges" Pyongyang to abide by its non-proliferation promises.— The Associated Press (@AP) September 9, 2016
China also openly opposed the tests by North Korea, which Japan calls an "outlaw nation."
BREAKING: South Korean president: North Korea's 5th atomic test an act of "fanatic recklessness."— The Associated Press (@AP) September 9, 2016
World leaders are condemning the tests. South Korea called it an act of reckless.
Friday's explosion was so massive that it was first believed to be a 5.3 magnitude earthquake. It is North Korea's strongest nuclear test to date, estimated at about 10 kilotons.
This is North Korea's fifth nuclear test since 2006 and its second test this year.
The Associated Press contributed to this story.
WATCH: For the news you need to start your day, check out our 60 Second Circa.