Tourists are being warned to avoid swimming in the sea off Koh Lanta island in Krabi province following reported sightings of the deadly Portuguese man o’ war.

On Aug 1, a Thai tourist posted on her Facebook that she had been stung by a sea animal resembling a jellyfish while she was walking along a Koh Lanta beach.

The photos she uploaded indicated that the creature was a siphonophore.

The chief of the Lanta Islands National Park said on Wednesday that he had been informed last week of the presence of the deadly siphonophore, also called Portuguese man o’ war, by several local hotels in Ko Lanta district.

He then told hotels and local government administrations in the area to warn tourists about the creature.

Portuguese man o’ war are not usually found in Thailand but some have been known to appear along the Thai coast during the monsoon season, the chief said. The sting can affect the nervous system and heart and cause severe pain. People are strongly advised not to touch them directly.

The best treatment if stung is to pour vinegar on the affected area and seek medical advice immediately.