BEIJING, Sept. 3 (Xinhua) -- China has started monitoring the radiation levels in its northeastern border areas in an emergency response to a nuclear test conducted by the Democratic People's Republic of Korea (DPRK).

The National Nuclear Safety Administration of the Ministry of Environmental Protection (MEP) initiated the emergency response at 11:46 a.m. Sunday, MEP said.

"At present, the automatic radiation monitoring stations in the provinces of Heilongjiang, Jilin, Liaoning and Shandong are functioning properly," the ministry said.

The China Earthquake Administration reported that a magnitude 6.3 earthquake struck the DPRK at 11:30 a.m. with an epicenter depth of zero km, saying that it might have been caused by explosion.

The DPRK's central television announced Sunday that the country had successfully detonated an H-bomb, a hydrogen bomb that can be carried by an intercontinental ballistic missile.

China's Foreign Ministry has issued a statement expressing firm opposition to and strong condemnation of the test.