Shortly after North Korea conducted what’s believed to be its first successful test of a hydrogen bomb (and its sixth nuclear test in total), China’s Nuclear Safety Administration said on Sunday that it would begin emergency monitoring for radiation along its northeastern border with North Korea, according to Reuters.

The emergency response was set at “level 2,” the second-highest grade on a four-tier system, according to the Times of Japan. The NSA did not indicate whether any radiation had been detected.

“’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.”

Earlier in the day, the presidents of China and Russia agreed to “appropriately deal with” North Korea’s sixth and most powerful nuclear test, according to the South China Morning Post. Beijing strongly condemned Pyongyang’s actions and threatened to work with the United Nation’s Security Council to add sanctions. The agreement came as Chinese President Xi Jinping met his Russian counterpart Vladimir Putin on Sunday night in Xiamen, Fujian province, ahead of Monday’s BRICS leaders’ summit, according to the SCMP.

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

Here’s more from the SCMP:

“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.’”

As one analyst who spoke with the SCMP suggested, the North may have timed its nuclear test to coincide with the BRICS conference that begins tomorrow in Xiamen. World leaders from some of the world’s largest emerging-market countries have traveled to China for the conference, and by testing the nuke Sunday, not only did the North overshadow the conference, which was supposed to be about economic issues, but it also provided world leaders with a first-hand look at its nuclear capabilities.