The U.S., Australia and U.K. have issued warnings for travelers in Vang Vieng after several tourists died in a suspected methanol poisoning outbreak.

The Laotian government on Saturday officially acknowledged the mass poisoning that has killed at least six tourists, pledging it would bring perpetrators to justice

The NHS warns that as little as 4ml of methanol can cause hallucinations and blindness. Half an hour to two hours after consuming methanol symptoms include drowsiness, confusion and irritability. Later symptoms include dizziness, vomiting, severe abdominal pain and diarrhoea.