Heyuan city police said the 120-metre (390-foot) section collapsed early on Friday morning.
China’s Xinhua News Agency said two nearby security guards rescued a 44-year-old man but two other people are still missing.
Dramatic footage aired on state broadcaster CCTV showed two arches of the six-arch bridge, which spans the Dongjiang river in Guangdong province, falling apart within seconds.
The cause of the collapse is under investigation but it came as southern China was battered by heavy rain which has brought flooding. At least 61 people have died.
In Longyan City in the Fujian Province, a landslide swept cars away and one man was trapped in his vehicle.
A local resident who went to the market was buried by the landslide.
His family could not reach him by phone and there was no response from him when rescuers shouted his name.
His rescue is still underway and his condition remained unknown, according to CCTV.
Hundreds of homes and businesses have been evacuated amid the heavy rains, affecting more than two million people across southern China.
More than 20,000 homes in the south-west region of Guangxi are without power, the state-run China Daily newspaper reported.