China today expressed "firm opposition" to the nuclear test conducted by North Korea, believed to be its most powerful atomic explosion ever. State-run Xinhua news agency briefly quoted a Chinese Foreign Ministry statement "firmly opposing" the test. Earlier, North Korea's state-run television said the country has conducted a nuclear warhead explosion test. This is the country's fifth atomic explosion and believed to be its most powerful ever. Monitors detected a 5.3-magnitude "artificial earthquake" near its main nuclear site this morning.