South Korean President Park Geun-hye called it an act of “self-destruction” and suggested this blast could be almost twice as strong as its last nuclear test – believed to be a hydrogen bomb - in January.
This test’s blast had a yield of about 10 kilotonnes. To compare, the bomb dropped by the US on Hiroshima in 1945 had a yield of around 15 kilotonnes.
The test has sparked fears the country could be a step closer to having a useable nuclear weapon.
China said they were opposed to the test and urged North Korea to avoid further action while the US warned of “serious consequences”.
The White House said President Barack Obama had spoken to both the South Korean and Japanese leaders about the country's actions.
A statement from press secretary Josh Earnest said Mr Obama had "reiterated the unbreakable US commitment to the security of our allies in Asia and around the world".
He said: "The president indicated he would continue to consult our allies and partners in the days ahead to ensure provocative actions from North Korea are met with serious consequences."
South Korean president Ms Park said the test was a "grave challenge" to the international community that would "only earn more sanctions and isolation" for the North.
"Such provocation will further accelerate its path to self-destruction," she said.
