Venomous Portuguese man-of-wars stung two children Tuesday on Fire Island, sending one of the young boys to the hospital, Suffolk County police and Islip Town officials said.

A 7-year-old was stung on the hand in Kismet around 3:08 p.m. and taken to Southside Hospital in Bay Shore. Another boy, 4, was stung earlier in the day at 12:17 p.m. in Davis Park, marine bureau Sgt. John Vahey said.

Another person was stung on the Davis Park beach but declined medical assistance, officials said.

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Man-of-wars, a colony of organisms with long tentacles that can sting, have also been spotted in Cherry Grove and Fire Island Pines, said Elizabeth Rogers, a park ranger for the Fire Island National Seashore.

They are carried by wind and currents, and can appear in the North Atlantic when the water is warm and the winds are out of the southwest. In 2013, about 50 were spotted beached in the East End.

"They're pretty rare," said Vahey, who has worked on Fire Island 36 years. "It's really only my second time I've heard of them on Fire Island."

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Islip Town public information officer Tracey Krut said the injured boy in Kismet touched the man-of-war on the beach. He was taken by boat to Bay Shore and then taken to the hospital. His condition is not known.

"He's unfortunately in a lot of pain," Krut said.

Islip ordered purple flags to be posted on the west and east sides of Kismet and at the main lifeguard station warning people that dangerous marine life had been spotted.

Beach staff will be on alert Wednesday.

"We'll be checking everywhere," Krut said.

The Fire Island Seashore has not posted a swimming advisory, but swimmers should stay away from man-of-wars and report sightings to lifeguards or park police.

Earlier this week, man-of-wars were spotted along the Jersey Shore.

"I haven't seen any yet," Southampton Town Trustee Edward Warner Jr. said, "but that doesn't mean they're not going to be here any day."