North Korea's nuke test set off a blast more powerful than the bomb dropped on Hiroshima.
"Firmly opposing" North Korea's fifth nuclear test, close ally China today lodged a diplomatic protest with the reclusive state and asked it to honour its commitment to denuclearisation and halt any move that could "aggravate the situation."
"We strongly urge the Democratic People's Republic of Korea (DPRK) to honour the commitment to denuclearisation, abide by the relevant UN Security Council resolutions and halt any moves that could aggravate the situation," China's Foreign Ministry said, using the country's official name.
"China will, along with the international community, keep working toward the goal of denuclearisation of the Korean Peninsula and commit to settling problems through the six-party talks," it said in a statement.
The ministry's spokesperson Hua Chunying told reporters that a senior official will lodge representation with South Korea.
North Korea's state-run television reported the country has "successfully" conducted a nuclear warhead explosion - its fifth and more powerful than it has earlier conducted - after monitors detected a 5.3-magnitude "artificial earthquake" near its main nuclear site this morning.
The test, which comes eight months after the last one, was expected to further tighten United Nations sanctions.
Chinese analysts say North Korea resorted to the fifth test as it was increasingly getting under pressure because of military exercises between the US and the South and also due to the proposed deployment of Terminal High Altitude Area Defence (THAAD).
China too is worried over the deployment of modern weaponry close to its borders on the Korean peninsula.
Asked if China knew about the test beforehand, Hua said she has "no information", but added developments on the Korean Peninsula this year have seriously damaged peace and stability and gone against the common expectation of the international community.
"As to the possible sanctions to be adopted by UN Security Council... (China) has always been earnestly observing and implementing relevant UNSC Resolutions and we will continue our position of opposing militarisation of Korean peninsula and take part in relevant negotiations in UNSC in a responsible attitude," she said.
But any unilateral action would be a dead end, making the situation more tense and complicated, she added.
Soon after the explosion, China ordered radiation monitoring in its border region with North Korea.
National Radiation Environmental Data Evaluation System said it has not detected any abnormal signs of radiation.
Chinese residents living near the border said on social media that they felt a strong tremor similar to when North Korea conducted a nuclear test in January, Hong Kong-based South China Morning Post reported.