Vehicles plunged into a river after the bridge they were riding on was smashed by a fallen rock from a nearby mountain early Saturday in Wenchuan County, the epicenter of last year's devastating earthquake. Casualties were not yet known, local officials said. The Chediguan Bridge is called a lifeline for the reconstruction of Wenchuan. The accident took place at about 5 a.m. when the fallen rock hit a pier, damaging the bridge. Riding cars fell into the Minjiang River below, said an official with the information center of Wenchuan County, Aba Tibetan and Qiang Autonomous Prefecture. 'It is not clear how many vehicles and people fell into the river,' said the official, explaining that the accident site is out of communication network. The bridge is part of the No. 213 national highway, a major traffic line linking Wenchuan to other areas. The highway, which plays a key role in restoring local tourism and production, was interrupted. More than 10,000 vehicles pass the bridge, which reopened to traffic in May, every day. An 8-magnitude earthquake struck Wenchuan County on May 12, 2008, leaving about 87,000 people dead or missing and injuring more than 370,000 others. 