Witnesses said the bridge fell into the Tongkou River during a rainstorm just before noon, local time, taking 10 vehicles and two passenger buses with it, the South China Morning Post reported.
Rescuers were at the scene in Sichuan province, aiding survivors.
Health officials said at least three people had been pulled out of the water, two in serious condition and one person with only minor injuries.
Photos posted on social media show an entire section of the Qinglian bridge wiped away in the swollen Tongkou River.
The two-lane bridge was built in 1967. Construction on a replacement was already under way at the time of Tuesday's collapse.
Heavy rain has been forecast for most of northern China this week.