BANGKOK - A 20-year-old German tourist has died after being stung by a poisonous box jellyfish off the popular island resort of Koh Samui, police said on Wednesday, the third known fatality in Thailand in just over a year.

The woman was pronounced dead late on Tuesday at a private hospital on the island after the attack during a nightime swim at Lamai beach. “Doctors said she died due to poison from a box jellyfish,” Lieutenant Thanakorn Patnankaew, a tourist police officer on the island, said. He added that local officials have since travelled to nearby beaches to warn tourists to be more cautious while swimming, though such stings are rare.

The German Consulate in Phuket confirmed that one of its citizens was killed due to a fatal jellyfish sting but could provide no further details.