A dream Overseas Experience has turned to tragedy for three young New Zealand women after food poisoning killed one and left the other two in hospital.

Sarah Carter, 23, died on Sunday, reportedly after eating a seaweed delicacy at a market in Chiang Mai, Thailand - just hours before her mother could get to her bedside.

Her friends Amanda Eliason and Emma Langlands, both 23, also suffered food poisoning and were last night still in Chiang Mai Ram Hospital.

Amanda remained in the intensive care unit while Emma was yesterday moved into her own room and was now eating.

"We've just been on a rollercoaster from hell," Emma's father, Richard, said last night. "Three of them went over, but one's not coming back. It's just horrific. These girls are so beautiful, professional and sensible. It's a terrible, terrible tragedy.

"I just can't understand how this happened ... they're all such amazing, hugely intelligent girls."

The three friends - who were on their OE after finishing their studies at Wellington's Victoria University - were rushed to hospital last Friday when they became ill after eating what is thought to have been toxic seaweed.

Two days later, Sarah was dead.

Yesterday her father, Richard Carter of Auckland, told stuff.co.nz that his daughter had "touched the hearts of everyone she knew".

He had spoken to her when she was first admitted to hospital. "It appeared to be just bad food poisoning. She appeared withdrawn and not sounding that good, but seemed all right," he said. "But within an hour of our conversation the thing just spread to her heart and strangled her heart."

Sarah's mother, Anna, had earlier rushed to be by their daughter's side after getting the call that Sarah was sick in hospital. She was in transit when her husband called to tell her that their daughter had died.

A former student at Auckland's Macleans College, Sarah studied chemistry at university and had been working at Wellington accounting firm BDO Spicers for the past year.

Last night, Sarah's 19-year-old brother, Ryan, was on his way to Bangkok to be with his mother.

Richard Langlands said his daughter Emma and Sarah were due to fly back in time for a wedding in Napier this weekend.

Mr Langlands said the three girls met at Victoria University and had been best friends for five years.

"My heart just goes out to Sarah's mum and dad and family because we've been living a nightmare. My daughter said she was the least affected, but in the next breath she asked, 'my friends are seriously ill, what can I do?'

"All she wanted to do was help Amanda and Sarah."

Emma's mother and brother have flown to Thailand.

Mr Langlands said he understood that a Thai travel agent found the girls sick in their hotel room and took them to the hospital.

He said the family was "extremely proud" of Emma because she had just finished a law degree at Victoria University and had got a job at law firm Bell Gully in Wellington.

Emma's grandfather, Bill Langlands, said his granddaughter was recovering well.

"She's started eating solids again, which is good. I think she's getting better quite quickly. For some reason she didn't get as sick as the other two, which is really lucky."

Mr Langlands said he spoke to Emma last night.

"She's doing really well and it was good to hear from her, but she's very upset about losing her friend. They were very close, it's just a tragedy."

Amanda Eliason's parents, Peter and Kay, from Kaponga, 19km southwest of Stratford, flew to Thailand on Monday to be with their daughter, who is recovering from emergency heart surgery in intensive care.

"We're taking each day as it comes...They won't allow her to fly (home) until they are very sure that - because of the heart- she's very ready to fly," Mrs Eliason told Radio New Zealand.

She said doctors had taken blood samples but were still unsure what caused the illness.

"It seems to have affected the blood pressure. The blood pressure went very low and [there were] complications with the heart, the heart is not pumping right," she said. "I think there was a fever as well although Amanda doesn't talk about the fever. She's been conscious the whole time."

Ms Eliason had been working at the Ministry of Economic Development in Wellington before going on holiday to South East Asia with her two friends.

Amanda's grandmother told Radio New Zealand Amanda had undergone the surgery at the weekend.

"Amanda is improving. The procedure that they inserted into her heart has been removed yesterday and she is making progress, but she will be some little while before they can bring her home."

Last night, she told the Herald that the past few days had been difficult.

"It's just been so sad. They were really good friends. They had all met at university and this was their big OE."

She had never met Sarah, but had heard good things about her from her granddaughter. She said the hospital told her Amanda's condition was improving.

Asked how the families were coping following Sarah's death, Mrs Eliason said it was a struggle.

"Our thoughts are with Sarah's family at the moment and also for the other two girls. It's been so sad but we are also very grateful that we still have Amanda and Emma. I'd say that they've got a tough road in front of them."

Speaking from Thailand last night, Emma's mother, Margaret, said she was pleased her daughter was recovering but out of respect to Sarah's family she did not wish to comment further.

On a memorial page made in Sarah's honour, family and friends paid tribute and offered condolences to her parents and siblings Ryan and 17-year-old Nicole.

One friend said: "You'll be the brightest star in the sky. Heaven has a new angel."

Services to remember Sarah are being planned in both Auckland and Wellington.

* There are several types of edible seaweed used in many countries.
* The high iodine content can produce iodine toxicity if large amounts are consumed.
* Rotting seaweed is also a potent source of hydrogen sulfide, a highly toxic gas which can cause vomiting and diarrhoea, but is rarely fatal.
* Most edible seaweed is marine algae - most freshwater algae is toxic.While marine algae is not generally toxic, some do contain acids that irritate the digestion canal, while others can have a laxative effect.
* Is a staple food in most parts of Asia and is used in soups, salads and as a side dish.
* Recognised in many Western countries, as being used in sushi and in spirulina.

- Additional reporting: NZPA