New US Secretary of State John Kerry faced his first global crisis Tuesday as North Korea defied UN resolutions to carry out its third nuclear test.

Just 12 days into his tenure as America's top diplomat, Kerry found himself making late night calls to Asian counterparts after Pyongyang went ahead with an underground detonation of a nuclear device.

"The DPRK did inform us at the State Department of their intention to conduct a nuclear test, without citing any specific timing prior to the event," State Department spokeswoman Victoria Nuland told reporters. "We were advised."

But she would not say how much notice Pyongyang gave before conducting what US intelligence said was "probably... an underground nuclear explosion" of "approximately several kilotons" at its Punggye-ri nuclear test site.

"I'm simply going to tell you that it was prior to the event," she said, adding the warning came through channels put in place as Washington and Pyongyang do not have diplomatic ties.

Nuland stressed that Washington had again told North Korea, also known as the Democratic People's Republic of Korea (DPRK), in the "strongest terms" that it opposed any nuclear test.

The United States is now pushing for "consequences" at the United Nations, Nuland said, confirming that another layer of sanctions would be one option.

Kerry only took over as secretary of state from Hillary Clinton on February 1 but, with the threat of a North Korean nuclear test looming, he was briefed on the situation as soon as he arrived at his desk.

"He was well-prepared in advance," Nuland said.

Kerry first spoke with his South Korean counterpart Kim Sung-Hwan late Monday US time, and then placed telephone calls to Japanese Foreign Minister Fumio Kashida and China's Yang Jiechi early Tuesday.

He was also trying to consult with Russian Foreign Minister Sergei Lavrov. Russia is also a member of the six-party talks which has been trying to persuade North Korea to abandon its nuclear program.

Kerry stressed in his calls "the need for a strong and swift response from the international community," Nuland said.

North Korea's nuclear ambitions could have profound implications for Washington which has defense treaties with South Korea (ROK) and Japan, under which the US is obligated to support them if they come under attack.

Kerry had "reaffirmed our defense commitments to the ROK and Japan, which... include the security provided by our extended deterrence commitments, including our nuclear umbrella and our conventional forces," Nuland said.

North Korea is already one of the most isolated countries in the world, and has been hit by a slew of sanctions to try to force it to rein in its nuclear program, and there are questions about how much more can be done.

But Nuland said "the US had found that internationally there was "quite a bit more that we could squeeze in terms of the DPRK's access to international finance ... in terms of cutting off its proliferation activities."

The US and its partners "are looking at the full suite of options to try to get the DPRK to change course," she added as the focus turned to efforts at the UN Security Council on how to respond to the test.

Last week in his first public comments about North Korea as secretary of state, Kerry warned the expected nuclear test would only lead to a "greater potential of conflict" and do nothing to help the country's stricken people.

"The people of North Korea are starving," Kerry told a group of young students visiting the State Department.

"They desperately need to become more open and connected to the world instead of harboring some of the worst gulags in the world where people are tortured, and forced labor."