SAO PAULO, Brazil - Swarms of jellyfish stung nearly 300 swimmers looking to cool off from a heat wave in a southeastern beach city, Brazilian media reported Sunday.

At least 15 people including children and teenagers were treated in Praia Grande for severe stings, doctor Adriano Bechara told the Tribuna newspaper, though their lives were not in danger.

Fire Capt. Atila Gregorio Ribeiro Pereira said the jellyfish were Portuguese man-of-war, which have long tentacles but are not too dangerous unless the victim has an allergic reaction, according to the Folha online news service.

Many of the injured arrived at medical centers Friday and Saturday crying from the pain of the stings, paramedic Claudio Casadei told Tribuna. Most were treated and released.

Authorities blamed an extreme heat wave over the southeastern region for the swarm in the shallow waters off Praia Grande.

Hundreds of thousands of Brazilians flock to the country's beaches every year during the holiday season.