Thai experts have dismissed allegations a toxic insecticide caused the sudden death of 23-year-old New Zealand tourist after she fell ill in her Chiang Mai hotel, the Bangkok Post reports.

Sarah Carter, 23, became violently sick on February 3 while staying at the Downtown Inn in Chiang Mai and died a day later.

Her two friends and travelling companions, Emma Langlands and Amanda Eliason, also fell ill but later recovered.

An investigation aired by TV3's 60 Minutes showed trace elements of the chemical chlorpyrifos, used to kill bed bugs, were found in the hotel room Ms Carter was staying in.

United Nations scientist Ron McDowall, who carried out tests on behalf of TV3, said the symptoms suffered by Ms Carter and the other tourists who died suggested they were killed by over exposure to the chemical.

But Chiang Mai Public Health Office deputy chief Surasing Visaruthrat told the Bangkok Post the investigation's conclusion "carries little weight".

Thorough checks conducted by the doctors when the three tourists were admitted to the hospital found no traces of insecticides and an autopsy found no toxic substances in Ms Carter's body, he said.

"We can't jump to a conclusion that toxin exposure was the cause of the death because the substance was allegedly found in the hotel room alone, not in the victim's body."

Dr Surasing yesterday chaired a meeting of the investigation team. The meeting, attended by doctors and experts from various agencies, ended with no conclusion on the deaths.

Test results of samples collected from the victims' bodies were sent back from laboratories in the United States and Japan, the Bangkok Post reported.

Sarah Carter's father, Richard, said TV3 had presented a strong case chlorpyrifos had caused his daughter's death.

The 60 Minutes investigation showed teams of Thai workers intensely cleaning rooms on the fifth floor of hotel, where Ms Carter and her friends became ill.

Mr Carter believed this was an attempt by the Thai authorities to get rid of evidence on her death in order to minimise damage to the country's lucrative tourism industry.

Green Party toxics spokesperson Catherine Delahunty yesterday called for Government to consider banning chlorpyrifos in New Zealand.

A kiwifruit worker was hospitalised in 2008 after being accidentally sprayed with Lorsban, in which the active ingredient is chlorpyrifos, she said.

"It is very worrying that this highly toxic chemical is still being used in New Zealand.

"Now it has been implicated in the deaths of tourists in Thailand, we must look more closely at its use here in New Zealand. Other countries have banned its use, particularly in homes and gardens.

"If it is dangerous in our homes, it's also dangerous to use in growing our food, and in the workplace."

Environmental Risk Management Authority guidelines show chlorpyrifos is acutely toxic to humans, very toxic in aquatic environments and toxic in soils.

Ms Delahunty said keeping it in use in New Zealand compromised the country's "clean, green" brand.

"Our livelihoods depend on our clean, green brand. We cannot afford to sacrifice our environment and our people for the sake of saving a few bucks by using an acutely toxic insecticide."