Phangan acting district chief Kasitdet Thongchu on Monday asked local administrative authorities andbeachside hotels to post signs warning of poisonous jellyfish and prepared first aid in case they are stung by them.
The measures followed the death of the five-year-old boy from France.
Yongyos Thammawut of the provincial public health office in Surat Thani said the boy went into shock from stings from the poisonous tentacles of a box jellyfish while with his parents on Khuad beach Saturday. He died as his parents and a guide were taking him to Phangan hospital for treatment, Dr Yongyos added.
The case was reported to the provincial public health office in Surat Thani on Monday.
The beach is popular for swimming and snorkelling.
The boy became entangled in the box jellyfish's long tentacles, which ran 20 cm deep. The jellyfish
surrounded and attacked by box jellyfish when he was on the water which was 20 centimetres long, Dr Yongyos said. Fully grown box jellyfish, some of the most-poisonous animals on earth, can reach three meters long.
They can be found seasonally off the beaches of Ko Lanta and Haad Nopparatthara-Mu Ko Phi Phi National Marine Park of Krabi province, Nam Bor bay in Phuket province, Cha-am beach in Phetchaburi province, and some beaches on Tao, Samui and Phangan islands.