The civil defense office in the Pacific coast state of Oaxaca said people from the town of Santos Reyes Nopala were walking over the bridge to get to a party when the structure failed.
The injured included 12 adults and 11 children. Many were taken to a hospital in the nearby beach resort of Puerto Escondido.
Such bridges are not uncommon in rural Mexico. Most are supported by a combination of steel cables and wooden planks, but some are built with ropes. It was not clear which type of bridge was involved in the collapse.