The Chinese Army has been on standby since March for an emergency by massing troops and fighter jets at the border with North Korea, the Washington Times quoted a U.S. government official.
China's official Global Times carried the story prominently on Wednesday.
Chinese warships conducted live-firing drills in the West Sea, where South Korean and U.S. forces were engaged in a joint annual exercise, the daily said.
But Chinese military activities were concentrated in Jilin Province, which shares the longest border with the North. Forces were reportedly ordered to raise the alert status to the highest level on March 19.
"Large groups of soldiers were seen on the streets in Ji'an, a city in Jilin, amid reports that the [Army] had been ordered to combat readiness status," the daily added. "Heavy armored vehicles, including tanks and armored personnel carriers, were reported moving near the Yalu [Apnok] River that separates China from North Korea."
A diplomatic source in Beijing said, "Whenever the crisis deepened on the Korean Peninsula, since the North's second nuclear test in 2009, China has reinforced its troops along the border. Amid escalating threats from North Korea, it's highly likely that Army has moved troops from the Shenyang Military Region," which is in charge of the border.