Kok Phi Phi National Park chief Worapoj Lomlim heard from his own rangers and officials at Haad Nopparat Thara that large schools of Chrysaora jellyfish had been seen off popular adjoining beaches on Koh Kai and Thale Waek and at Koh Poda.
A particularly large school of Chrysaora was infesting diving sites around Koh Kai.
Worapoj urged tourists to be careful.
Tourist boat operators were instructed to advise their customers accordingly and to be prepared to perform emergency first aid.