Following the expo's opening on Wednesday, many tourists who bought food and drinks at the event later suffered diarrhoea caused by improperly-cooked food, a tambon-level health official who participated in a local food-inspection team said.

The official, who asked not to be named, said his team flashed their badges at the organiser before asking to inspect food at the expo but they were turned down, as the organiser thought they wanted free access to the event.

Dr Surasing Wisarutarat, deputy chief of the Chiang Mai public health office admitted there were cases of diarrhoea but said it had not been proved yet that they were the result of food sold at the expo. He said those falling ill were a small proportion of the 15,000 expo visitors each day. Surasing said the organiser only let food trucks deliver in the morning, before the daily opening, while it was very hot throughout the day, so if vendors did not take good care of food products, that might lead to problems.