CHENGDU -- A 5.0-magnitude aftershock jolted Pengxian County of southwest China's Sichuan Province at 3:28 p.m. Monday, the China Earthquake Networks Center said.
The epicenter of the aftershock is at 31.4 degrees north latitude and 103.8 degrees east longitude in Pengxian, some 20 kilometers from the provincial capital of Chengdu, according to the center.
Xinhua reporters in Chengdu and neighboring Mianyang city said the strong tremor last for about 10 seconds.
Xinhua reporter Wang Yang in Wenchuan county seat, epicenter of the 8.0-magnitude quake on May 12, said over his cell phone that the aftershock was also felt in Wenchuan.
"It is the strongest aftershock I have experienced in three days. Scared residents rushed out of shaking buildings and tents, gathering in streets," said Wang.
"The volunteer who drove us to Wenchuan also escaped from his car when the aftershock happened," he said.
Earlier on Monday, a strong aftershock was felt on the dam of the Tangjiashan "quake lake" at around 11:04 a.m. Monday, a Xinhua reporter at the site said.
The tremor sent rocks rolling down the surrounding mountains and splashing into the quake-formed Tangjiashan Lake in Mianyang City, one of the hardest-hit areas in the May 12 earthquake.
The earthquake administration has not defined the magnitude of the aftershock and its impact on the dam is under surveillance.
"I don't see any imminent danger despite the aftershock and the swelling quake lake," Xinhua reporter Li Gang said via a mobile phone text message at 12:21 p.m.
Li was on the dam of Tangjiashan Lake, formed after the May 12 earthquake, with the People's Liberation Army soldiers to cover the drainage process.
"Besides, the soldiers are all veteran repairmen and peril removers," he said.
More than 100 soldiers of the hydropower force of the armed police, apparently used to the innumerable aftershocks, continued digging for a new spillway at the bottom of the lake's dam.
The new spillway would hopefully be connected with a drainage channel that has been operating since Saturday morning to accelerate drainage of the quake lake.
Although Monday's aftershock was clearly felt by everyone on the dam, it did not seem as powerful as Sunday's 4.8-magnitude aftershock that caused massive landslides on the mountains surrounding the Tangjiashan lake.
Yet in Dujiangyan City, another hard-hit area in Sichuan Province, Monday's aftershock sent a big rock about 1.5 meters wide and 1 meter in height rolling down a mountain and smashing the windshield of a Mitsubishi cross-country vehicle. A PLA soldier was injured.
China is still on the alert as the water level in Tangjiashan Lake reached 742.58 meters above sea level as of 8 a.m. Monday, a rise of 0.92 meters in 24 hours.
Military engineers have fired short-range missiles to blast boulders in the channel to accelerate drainage. By Monday noon, the drainage speeded up to 50 cubic meters per second, but still far slower than the average influx of 115 cubic meters per second.
The largest of more than 30 quake lakes in Sichuan after the quake, Tangjiashan threatens some 1 million residents living in the lower reaches of the river once it overflows.
More than 250,000 people in low-lying areas in Mianyang City have been relocated under a plan based on the assumption that one-third of the lake volume breached the dam.
