Another two Australians are among a total of seven people hospitalised, and the federal government is providing consular assistance to two families.
It comes after two Australians died in Laos from a suspected mass ethanol poisoning.
The father and grandfather of two of the Australians, David Sandoe, said his daughter Tanya and her daughter Georgia had been discharged from hospital and received confirmation they were medically fit to travel.
"Like everyone else when this news broke we all thought back to what recently happened in Asia which sends shivers down your spine, so we're so grateful and very fortunate," he told Sky News on Monday.
It was a horrific experience, he said, describing a late-night call from his daughter telling him she had been taken to hospital as "quite something else".
Georgia, in her late teens, suffered a seizure after drinking a cocktail, he said.
She had a pre-existing condition that affected her immune system which was a major concern, Mr Sandoe said, but the fear was quelled when he spoke to doctors in Fiji.
Tourism Minister Viliame Gavoka said it's an isolated incident that's being investigated thoroughly. (Mick Tsikas/AAP PHOTOS)
It was an isolated incident localised to one bar at one resort that was being thoroughly investigated, Fiji's Tourism Minister Viliame Gavoka said, reassuring travellers of their safety.
It was the only reported case in recent memory, Mr Gavoka said.
"While we understand the concern, we want to emphasise that the tourism experience in Fiji is typically very safe and we have acted immediately to try and discover the cause of what made these guests at this resort fall ill."
The resort's management had assured authorities they had not substituted ingredients or altered the quality of drinks, he said.
Warwick Fiji said it was aware of the news and was waiting for health authorities test results "to gather all necessary information" about the incident at its hotel.
"Please rest assured that we are taking this matter very seriously and are currently conducting a thorough investigation," it told AAP in a statement.
"We do not have conclusive details but we are committed to ensuring the safety and wellbeing of our guests."
Australia has revised its travel advice for Fiji, warning travellers to "be alert to the potential risks around drink spiking and methanol poisoning through consuming alcoholic drinks".
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