The Ministry of Environmental Protection said no radiation had been detected from the nuclear test by 10am yesterday based on meteorological data and more than 150 monitoring stations.
"North Korea's third nuclear test has not posed any threat to our people's health and our nation's environment," a statement on its website said. "We haven't detected any radiation from the nuclear test within our border."
The ministry said it had sent task forces to northeastern China, which borders North Korea, to enhance monitoring and take soil and air samples.
Data from 25 monitoring stations and 12 mobile spots in regions close to the test site showed that radiation levels were normal and within the daily average, the ministry said.
The ministry also quoted analysis by the China Meteorological Administration that if any radiation had been released, it would move toward the southeast and not have any impact on China.
People in Jilin Province, which shares a border with North Korea, said they felt a one-minute tremor at around 11am on Tuesday. Monitoring stations in South Korea detected an earthquake in North Korea with a magnitude of 4.9.
North Korea's KCNA news agency said the test had used a "miniaturized" and lighter nuclear device, indicating the country's capability to develop an A-bomb as a missile warhead.
China's Foreign Minister Yang Jiechi called in North Korea's ambassador to China Ji Jae Ryong later on Tuesday to lodge a solemn representation.
Yang said China was "strongly dissatisfied with" and "firmly opposed to" the nuclear test, according to a Ministry of Foreign Affairs press release.
The ministry said it was the firm stand of the Chinese side to bring about denuclearization of the Korean Peninsula, prevent nuclear proliferation and safeguard peace and stability in the region.
North Korea conducted similar nuclear tests in 2006 and 2009.
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