LHASA, Aug. 25 (Xinhua) -- A strong earthquake measuring 6.8 on the Richter scale rocked Zhongba County, Xigaze prefecture in Tibet at 9:22 p.m. on Monday, but no casualties have been reported.

    The epicenter was about 10 km underground at 31 degrees north and 83.6 degrees east, according to the China Earthquake Networks Center.

    Gerze and Coqen counties in Ali prefecture also felt the quake. But the county seats suffered no damage, said the regional earthquake bureau.

    A Zhongba county government worker said the quake was strongly felt in some townships and cracks had appeared in some buildings.

    Zhu Jiang, the Zhongba county's Communist Party boss, said they had contacted all 13 townships in the county. The townships reported no casualties for the time being.

    The official said special personnel dispatched by the county government had rushed to townships and villages to assess the situation and carry out disaster relief work.

    Zhu Quan, the regional earthquake bureau chief, said the tremor would have no effect on the Qinghai-Tibet railway, which is several hundred kilometers away from the quake zone.

    Zhongba, in the west of Xigaze with a population of 18,000 and covering 43,594 square kilometers, is located in an area with frequent quakes.

    A 6.7-magnitude quake occurred in the area in 2004, followed by a 6.5-magnitude on April 8, 2005, but both caused no casualties, according to the regional earthquake bureau.