The bridge over a river in Shaanxi province's Shangluo buckled at around 8:40 pm Friday (1240 GMT) "due to a sudden downpour and flash floods", state news agency Xinhua said, citing the provincial public relations department.
State broadcaster CCTV said nearly 20 vehicles and more than 30 people remained missing after the highway bridge collapsed into the river below.
All 11 confirmed victims were found inside five vehicles that had so far been recovered from the water, the broadcaster said.
Images on state TV showed a partially submerged section of the bridge with the river rushing over it.
Chinese President Xi Jinping has urged "all-out efforts" to find those still missing.
Large portions of northern and central China have been battered since Tuesday by rains that have caused flooding and significant damage.
China is enduring a summer of extreme weather, with heavy rains across the east and south coming as much of the north has sweltered in successive heat waves.
Climate change, which scientists say is exacerbated by greenhouse gas emissions, is making these types of extreme weather phenomena more frequent and more intense.
SD/PR