"We still do not know the full details around Renée's passing."
Tanagon Tammakan of the Phi Phi Island Police said the woman was on Phi Phi Island with a tour group, but refused to return with them.
"She remained on Phi Phi by herself and is believed to have drowned while swimming on Wednesday morning. However, details are still under investigation," he said.
He said the woman was found floating in Lo Dalum Bay by a Burmese worker on a boat, who notified police.
Tanagon said a hospital examination revealed no signs of violence and the doctor ruled the cause of death as drowning.
It was believed the woman had been dead for about six hours before she was found.
"She was identified because the tour group contacted police after receiving news reports that the body of a foreign woman had been found. They then confirmed her identity through her tattoos," said Lt Tanagon.
A Ministry of Foreign Affairs and Trade spokesperson said the ministry was aware of the death of a New Zealand woman in Thailand and "is providing consular assistance to family".