A jellyfish that can be extremely dangerous washed up on a Jersey Shore beach on Sunday.

Lifeguards spotted the Portuguese man o' war jellyfish on Sunday on Long Beach Island and are now warning swimmers to exercise extra caution. 

The Harvey Cedars Beach Patrol posted about the spotting on their Facebook on June 21.

"This morning we found a Portuguese man o' war washed up on the beach," the patrol posted. 

Also known as the "physalia," "floating terror" or "bluebottle," a man o' war's sting is said to be far more painful than that of a regular jellyfish.

"Physalia stings can be lethal, but are more frequently just excruciatingly painful," said Dr Lisa-Ann Gershwin, director of the Australian Marine Stinger Advisory Services. 

The man o' war has venomous tentacles that can grow to be as long as 30 feet, which it uses to paralyze and trap ocean prey.

Depending on the person, a man o' war's stings can cause extreme pain, fever, shock, lung and heart problems and in rare cases, death, reports say.

But a bigger mystery may be how the tropical jellyfish found its way to New Jersey.

Gershwin says this species is known to travel.

"Physalia can travel immense distances because of the way its sail sticks up out of the water. It literally sails the breezes around the world. Although it is generally associated with the tropics, it does occasionally turn up in far flung places," she said. 

A British beach was closed in 2008 after 10 man o' wars were found in the area.