New Zealanders travelling to Chiang Mai in Thailand should take preventive health measures following six mystery deaths in the city, including New Zealander Sarah Carter, the Ministry of Foreign Affairs and Trade (MFAT) says.

Ms Carter, 23, became ill last month while staying at the Downtown Inn in Chiang Mai, and died a day later.

Early reports suggested the cause of her death was toxic seaweed she had eaten, but food poisoning tests proved inconclusive.

Since her death a further five people have been reported as having died in similar circumstances around the same time.

A report by Thailand's Department of Disease Control found Ms Carter was one of three people to die as a result of myocarditis between January 9 and February 4 in Chiang Mai - the others were American Soraya Vorster, 33, and a Frenchwoman aged between 23 and 33.

An elderly British couple and a 47-year-old Thai woman staying in the same hotel as Ms Carter also died around the same time, in similar circumstances.

Chiang Mai Governor Pannada Disakul said their deaths were coincidental.

MFAT said in a travel advisory issued yesterday evening it was aware of the six unexplained deaths.

"The cause of death is unknown, and the results to date are inconclusive although there has been speculative media comment linking the deaths to local food markets."

The advisory warned travellers to take general preventive health measures, including paying attention to personal hygiene, eating only hot food and drinking clean water.

"Those who experience severe sudden multiple vomiting with or without diarrhoea, should seek medical attention immediately.

"The Governor and authorities in Chiang Mai have asserted that Chiang Mai is safe for tourists.

"However, in light of the lack of any clear explanation of the recent deaths, it is up to individual travellers themselves to determine the risks of travelling there."