Dr Thanuwat Tippinit, of the hospital on Koh Phangan, in the Gulf of Thailand, said today that nobody should swim in local waters at night in the wake of the tragic death of 31-year-old Chayanan Surin, a tourist from Bangkok.
Photographs of her torso and an arm showed the distinctive welts of the tentacles of a box jellyfish.
The box jellyfish is one of the world's most toxic animals and its stings usually cause victims to die quickly and in agony.
Khun Chayanan is believed to have been swimming in darkness about 8.15pm last night with friends off a beach on the holiday island when she was stung. She died at 9.30pm at the hospital.
A French boy aged five years old died on Koh Phangan from box jellyfish stings in August last year, Dr Thanuwat said today.
Experts say that the only treatment for box jellyfish is common vinegar. The vinegar does nothing to dull the pain but it does combat the toxicity. Without vinegar, the jellyfish stings continue to attack and destroy the victim's flesh.
Islands in the Gulf were in the news recently during the continuing trial of two Burmese workers on neighboring Koh Samui. The workers allegedly killed British tourist David Miller, 24, with a hoe then killed and raped his companion, Hannah Witheridge, 23, in September last year on Koh Tao, another nearby island*.
No box jellyfish fatalities have ever been recorded on Thailand's popular Andaman coast, centring around Phuket, which is on the opposite side of the Isthmus of Kra to the Gulf of Thailand and affected by different currents.
*An earlier version of the report erroneously put the murders on Koh Phangan.