Keep an eye out if you’re visiting Nahant Beach. Officials said the world’s largest species of jellyfish was spotted there last week.

Officials from the Department of Conservation and Recreation said lion’s mane jellyfish were seen in the area of Nahant Beach on Friday, prompting officials to post an advisory and put up purple flags that indicate the presence of dangerous marine animals on the beach.

“Biologists are en route to determine the appropriate hazard level and necessary additional precautions, if any,’’ the department posted on Facebook Friday morning. “All [beach] use is at-own-risk at this time.’’

The advisory was still in effect as of Monday afternoon, said Craig Gilvarg, a spokesman for the state’s Executive Office of Energy and Environmental Affairs. Officials have not received any reports of individuals getting stung by jellyfish in the state, he said.

Lion’s mane jellyfish are among the longest animals on the planet, said Peter Gawne, an assistant curator of exhibits at the New England Aquarium.

Their bell-shaped heads alone can stretch as wide as 8 feet. If they live in plankton-rich waters, Gawne said, they can grow to be as big as blue whales, which often span nearly 90 feet.

These jellyfish are commonly seen in the Arctic, Northern Atlantic, and Northern Pacific oceans, Gawne said. But the ones found in New England are usually smaller than their northern counterparts, with their heads only growing between 4 and 18 inches long.

“We see them frequently in the early summer months,’’ Gawne said. “We often see them in Boston Harbor right behind the aquarium.’’

The lions mane jellyfish are also frequently spotted in Scituate, said Carolyn Forde, an assistant harbormaster in Scituate.

“We see them as far north as Minots Light and all the way down to the North and South rivers,’’ Forde said. “They aren’t the enormous kind and are usually traveling alone, but we see them almost every time we go out on tours.’’

While the jellyfish can be easily found swimming in Scituate’s waters, Forde said they rarely wash up on shore and haven’t stung anyone recently.

If you do see them on the coast, officials warn to keep your distance. A sting from a lion’s mane jellyfish can cause temporary pain and redness, or trigger special allergies in some people.

“They can have a painful sting, but usually not scarring or life-threatening. People have a range of sensitivity to jelly stings," Gawne said.

Stings are not known to be fatal in healthy people, DCR officials said. But a person who has been stung over large areas of their body by an entire jellyfish, not just their tentacles, should seek medical attention.

Lion’s mane jellyfish were also spotted at Belle Isle Creek and Chelsea Creek on Saturday. Purple flags were put up at Constitution Beach in Boston, King’s Beach in Lynn, Revere Beach, and Winthrop Beach "to warn visitors of the jellyfish’s potential presence,’’ Gilvarg said.

“If a beachgoer encounters a lion’s mane jellyfish, they should move slowly up current and away from the animal to avoid tentacle exposure.’’ Gilvarg said. “If stung, flush the tentacles away from the affected area with clean seawater.’’

Caroline Enos can be reached atcaroline.enos@globe.com. Follow her on Twitter@CarolineEnos.