A survivor of the Thailand poisonings has been asked to supply more blood samples to help uncover the cause of five deaths in six weeks.

Amanda Eliason was left in intensive care after falling ill in a Chiang Mai hotel room together with friends Sarah Carter and Emma Langlands.

The 23-year-old pulled through after undergoing a heart procedure and is now back in New Zealand.

Her father, Peter Eliason, yesterday said Amanda would supply more blood for Thai health officials.

They have said the deaths of Sarah Carter, two other tourists and a local woman are "nothing more than coincidence".

A fifth death, at another hotel nearby, is so far unexplained.

Mr Eliason said that was very difficult to believe and Amanda hoped her blood samples could provide some clues.

"We just want to get to the bottom of it and stop the possibility of it happening in the future.

"When I was over there I asked how many similar cases they had and I was told, 'Not many'.

"You just wonder now what is being covered up."

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

It has since emerged that British pensioners George and Eileen Everitt and local woman Waraporn Pungmahisiranon died in similar mysterious circumstances in the same hotel within two weeks of Sarah.

And a fifth woman - 33-year-old America tourist Mariam Soraya Vorster - died three weeks earlier in similar circumstances, though she was not staying at the same hotel.

Tests on tissue taken from Sarah have now been sent to experts in the United States and Japan.

NZ Foreign Minister Murray McCully hopes to get information from Chiang Mai health authorities in the next few days.

"We're seeking whatever forensic information might be available and that's something we'll work our way through over the next few days," a ministerial spokesman said.

Mr McCully did not need to send Foreign Affairs and Trade officials to Chiang Mai because New Zealand had a "very good" official in the ambassador in Bangkok.

"He has been asked to ensure that we extract the required information."

- Additional reporting NZPA