There were no signs of the Portuguese man o' war on Saturday on Phi Phi Islands in Krabi, despite media reports that it had surfaced, a parks chief said.
Ratchanok Phaenoi, chief of the national marine park overseeing the archipelago, said a survey was conducted following news about the highly venomous hydrozoan being found at some beaches in neighbouring Phuket.
Staff failed to find the man o' war (Physalia physalis), but would stay on alert due to the potential danger they pose to tourists, said Ms Ratchanok.
The Portuguese man o' war has venomous microscopic nematocysts which deliver a painful sting powerful enough to kill fish and has been known to occasionally kill humans.
Found mainly in the Pacific Ocean, the man o' war is sometimes found in Thailand during the southern monsoon, said Ms Ratchanok.
Likely to sting: No signs of the Portuguese man o' war on Koh Phi Phi.