Sao Paulo - Thousands of flesh-eating piranhas have appeared along a river beach popular with tourists in western Brazil, attacking unwary swimmers.

A spokesperson for the municipal government of Caceres in Mato Grosso state says at least 15 people have been bitten in the past two weeks off Daveron beach.

Nobody has died, but some swimmers have lost toes, and the spokesperson says others have lost chunks of their legs and ankles.

Piranhas are common in rivers on the outskirts of the city, but this is the first time they have appeared in waters off the beach inside the city.

Large posters have been posted on the beach to warn swimmers about the fish. - Sapa-AP