A fifth tourist has died in Chiang Mai, Thailand, in circumstances eerily similar to New Zealander Sarah Carter's mysterious death - which health officials initially blamed on food poisoning.

Mariam Soraya Vorster, a 33-year-old from Berkeley, California who was working as a guide in Chiang Mai, died on January 11 - just over three weeks before 23-year-old Sarah died.

Ms Vorster's husband Tony Pandola told the Herald his wife was perfectly fit and healthy and became sick with symptoms of food poisoning before she died.

"I kept asking about the health department, or what the next steps would be with the restaurant," Mr Pandola said. "No one really seemed to know, and it turns out no one really did anything.

"Soraya had an autopsy at University Hospital in Chiang Mai on January 12 or 13 and we still have no results."

Ms Vorster's death is one of five in a six-week spell in Chiang Mai.

Local woman Waraporn Pungmahisiranon died two days before Sarah and British pensioners George and Eileen Everitt died less than two weeks later.

Those deaths were all in the same hotel - the Downtown Inn.

Mr Pandola said his wife was staying in a different hotel, but the symptoms were the same.

At a press conference in Bangkok yesterday, Chiang Mai Governor Pannada Disakul said: "We have to admit that these deaths coming one after another are nothing more than coincidence.

"We have done and will continue to do our utmost to make tourists confident in our city."

The press conference was told Mr and Mrs Everitt, 78 and 74, died within minutes of each other of heart attacks.

The couple's son Stephen Everitt yesterday told the Herald that was not a believable explanation.

"They had no history of heart problems or any other problems," said Mr Everitt from his home in Lincolnshire.

"They were active and healthy for their age and it has come as a total shock.

"And now they want me to believe they both had heart attacks at the same time. It doesn't make sense. How can it be coincidence?"

Yesterday's press conference, which did not include details of Ms Vorster's death, was told tests were still being conducted into Sarah's death.

Tests on tissue taken from Sarah Carter had been inconclusive and samples had been sent for analysis to the United States and Japan, said Dr. Pasakorn Akaraseri, of the Communicable Disease Department of Thailand's Ministry of Health.

He said there was no evidence to suggest that any of the deaths were as a result of the guests eating food bought at the local market or on the street.

Sarah and two friends - Amanda Eliason and Emma Langlands - became sick in the Downtown Inn in Chiang Mai on February 4. Sarah died in hospital two days later.

Amanda and Emma recovered and are now back in New Zealand.

Richard Carter, Sarah's father, said the press conference was a "fob off".

"It doesn't sound like there's any real investigation going on here.

"You start to wonder how many other deaths there have been that are being swept under the carpet."

Mr Carter said the New Zealand Government needed to put on more pressure to find out how many similar deaths there had been in the last few years so travellers could make informed decisions.

"At the moment it's pot luck. People head off on holiday and then 'bang' they're dead."

Foreign Minister Murray McCully said the comments from the press conference were "not wholly convincing and we intend to give them closer scrutiny".

"We will look into the matter further. I gather there is still some work being done of a forensic nature of some samples and we are looking forward to seeing that material too.

"It's clear that we need to ask some more questions."

Asked if the Government would launch its own inquiry Mr McCully said that was too early to consider.

"Let's not get ahead of ourselves, let's just ask the questions methodically as we go forward... Clearly the obvious questions need to be asked and answered fully."

- additional reporting Andrew Drummond, NZPA