At least 60 swimmers have been injured in a piranha attack on an Argentine beach on Christmas Day.

The attack involved more than 20 children, with one seven-year-old girl losing part of one of her fingers and another boy sustaining an open fracture to his hand by the shoal of meat-eating fish. Other victims suffered bites to their feet and hands by the palometas, a cousin of the piranha.

Swimmers had been trying to cool down in the 40C heatwave when some suddenly ran out of the water, bleeding and shouting for help, witnesses told La Capital newspaper. Paramedics were called to attend the scene and treat the most seriously injured by coast guards while police closed down the beach.

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Paramedic Gustavo Centurion described the fish as “very aggressive", the newspaper reported, which may have been a product of the sweltering heat.

Federico Cornier, the director of emergency services in the city of Rosario spoke on television and said: "This is not normal. It's normal for there to be an isolated bite or injury, but the magnitude in this case was great ... this is an exceptional event."

The piranhas are believed to have been attracted to the area by bait left behind by local fisherman at the popular Parana River beach in the city of Rosario, about 300 miles north of Buenos Aires.

The attack was described as a rarity by local government spokesman Ricardo Biasatti.