Two young women — one from the United States and the other from Norway — died after suddenly falling ill within hours of each other at a guesthouse on a tourist resort island in southern Thailand.

Police said Thursday they did not know the cause of the deaths, though various theories have circulated, including food or alcohol poisoning and toxic fumes.

The two women were staying on Koh Phi Phi, a popular destination for budget travelers. The American was identified by her family as Jill St. Onge, 27, a bartender and artist from Seattle, who died Sunday.

Norwegian media and the Web newspaper Andaman Times identified the Norwegian as Julie Michelle Bergheim, 22. She died Monday.

Both women, who stayed at the Laleena guesthouse but were not known to have been in contact with each other, suffered severe vomiting and stomach pains.

Another 19-year-old Norwegian woman staying with Bergheim also fell ill with the same symptoms but survived. She was recovering in intensive care at a hospital.

Doctors said the women died at a hospital on Phi Phi "due to dehydration and shock," Police Capt. Pantanan Santhong said.

"Right now, we do not have any further information on what happened and how it happened," Pantanan said. "We are investigating."

The bodies were taken to the Thai capital Bangkok for autopsies but no results were available Thursday.

St. Onge's fiance, Ryan Kells, who was with her, said in a blog entry they both became sick after eating dinner together, though he recovered.

Few details were available about Bergheim, who Norwegian media said came from Drammen, near Oslo. "I don't know if it was something she ate or if it was because she went out to party," guesthouse owner Asan Buntam said.