(creative commons/sweetie187)

Thousands of flesh-eating piranhas have infested a beach in western Brazil and bitten at least 15 swimmers.

Officials from the city of Caceres in Mato Grosso state said this is the first time they have had a problem with piranhas at the popular Daveron beach on the Paraguay river, where the aggressive fish began schooling about two weeks ago.

"People have got to be very careful. If they're bitten, they've got to get out of the water rapidly and not allow the blood to spread," firefighter Raul Castro de Oliveira told Globo TV's G1 website yesterday.

Elson de Campos Pinto, 22, was bitten on Sunday.

"I took a dip in the river and when I stood up, I felt pain in my foot," Pinto told G1.

"I saw that I had lost the tip of my toe. I took off running out of the river, afraid that I would be further attacked because of the blood. I'm not going back in for a long time."

The beach will remain open because it's an important attraction for tourists in Brazil's Pantanal region, known for its ecotourism, city officials said.

Every September, Caceres hosts what is renowned as Brazil's biggest fishing festival, a weeklong event that attracts 200,000 people for fishing tournaments and concerts.

The piranha attacks are not believed to hinder the tourism given the event is many months away, according to a city government spokesperson, Gonzaga Junior.

"Everyone knows there are piranhas in the region and have always taken the necessary precautions," he said.

"What is different this time is that they've appeared where they never appeared before."

Fewer people have been using the beach of late because of the recent piranha attacks.

It was deserted on Tuesday, a national holiday in Brazil, which would normally see the beach packed with people.

Officials have erected large signs with bold red letters warning swimmers of the risk: "Attention swimmers. Area at risk of piranha attacks. Danger!"

A local fisherman said that when he has thrown out a fishing net near the beach in recent weeks he catches several piranhas.

"I come here with my kids and I always see blood on the river banks," Hildegard Galeno Alves told G1.

"The worst is that the attacks are in shallow water, next to the bank."

Despite making his living off the river, Alves had no doubt about taking serious precautions around the infested waters.

"I would never even think of going in there," he said.