US President Donald Trump responded to the test on Twitter, saying North Korea’s “words and actions continue to be very hostile and dangerous” to the United States.

Trump said North Korea was “a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success”.

“South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!”

The test late Sunday morning triggered a 6.3-magnitude quake followed by a 4.6-magnitude tremor, and was felt throughout northeastern China.

“The Chinese government resolutely opposes and strongly condemns this,” the Chinese foreign ministry said after North Korea confirmed the test.

“We urge North Korea to recognise the determination of the international community to achieve a denuclearised Korean peninsula … and to return to the path of resolving conflicts through dialogue,” it said adding that China will continue to implement UN sanctions against Pyongyang in “comprehensive manner”.

China’s nuclear safety agency also started monitoring radiation levels in its northeastern border areas on Sunday.

“At present, the automatic radiation monitoring stations in the provinces of Heilongjiang, Jilin, Liaoning and Shandong are functioning properly,” Xinhua reported, citing the Ministry of Environmental Protection, which administers the safety agency.

Addressing a business forum hours after the test, Xi did not refer directly to North Korea but he did say the BRICS bloc should be more proactive in mediating geopolitical disputes. He also underlined the importance of the United Nations.

It was the third time Pyongyang had conducted a test just before a major diplomatic event for Beijing.

North Korea also carried out missile tests ahead of Xi’s meeting with US President Donald Trump in Florida in April and as China prepared to host a massive summit in Beijing in May to discuss its signature “Belt and Road Initiative”.

Beijing has long insisted that the main targets of Pyongyang’s aggression are the US and South Korea, but Zhang Liangui, a professor of international strategic research at the Communist Party’s Central Party School, said the timing of the tests suggested there was a “China factor” at play.

“North Korea makes a bold move every time China has a big event,” Zhang said.

He also said the international community had few options left to deal with Pyongyang.

“North Korea has sought to prove that sanctions don’t work and it does not want to go back to the negotiating table any more,” Zhang said.

“Now there are only two choices left: admit that we have failed in our goal of denuclearisation of the Korean peninsula or the US makes a military move.”

Zhang added that China and Russia’s different security interests would make it difficult for the two countries to achieve meaningful cooperation.

“Russia’s border with North Korea is not as [long as] China’s,” Zhang said. “This means Russia could tolerate a nuclearised North Korea and may even consider it as a way to contain the US. But the impact [of North Korea’s aggression] could be devastating to China.”

Lu Chao, director of the Border Studies Institute at the Liaoning Academy of Social Sciences, said North Korea had reached the peak of its provocation with its sixth nuclear test, and it was time for China to respond with even tougher measures, such as cutting oil supplies to Pyongyang.

“North Korea is determined to push ahead with its plan under the mistaken belief that once it has nuclear weapons, the US will be forced to concede,” Lu said.

“But the US and China will not recognise North Korea as a nuclear state.

“We need to take even stronger measures to ensure North Korea understands that it will pay an unbearable price if it continues with its reckless act.”

But Lu said China would likely oppose any unilateral action, and any further sanctions, such as cutting oil supplies to North Korea, would have to go through the UN Security Council.

Hong Kong-based military commentator Song Zhongping said the test was a great setback in efforts to rid the Korean peninsula of nuclear weapons.

“As the situation worsens, the United States will probably have to deploy tactical nuclear weapons in this region, otherwise it would have to allow Japan and South Korea to develop or possess nuclear arms,” Song said. “Either way, China would be surrounded by nuclear weapons and suffer the most.”