Four Australians are seriously ill in hospital in Fiji after staying at a five-star Coral Coast hotel resort, with what local authorities suspect is alcohol poisoning.

However the resort management responded on Monday saying the drinks in question did not contain “substituting ingredients”.

The Department of Foreign Affairs and Trade (Dfat) confirmed through a spokesperson on Sunday evening that it was providing consular assistance to two Australian families in Fiji, but declined to provide further details.

Seven foreigners including four Australians and an American were hospitalised after drinking cocktails at Warwick Fiji, local health officials said on Sunday.

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The hotel guests had been taken to hospital on Saturday night suffering “nausea, vomiting and neurological symptoms”, Fiji’s health ministry said.

They fell ill after drinking a cocktail prepared at a bar in the resort about 60km west of the capital, Suva.

The Guardian understands one of the four Australians has returned home.

A ministry spokesperson said the guests, aged from 18 to 56, included four Australians, one American and two foreigners who lived in Fiji but whose nationalities were not given. All seven were initially taken to the nearby Sigatoka hospital.

Due to the severity of their conditions, they were later transferred to the larger Lautoka hospital on the island’s west coast, the ministry said.

Fiji’s deputy prime minister and minister for tourism and civil aviation, Viliame Gavoka, said in a statement that they have been working with the resort, who have assured them that the drinks were not tampered with.

“The resort management has assured us that they have not engaged in practices such as substituting ingredients or altering the quality of drinks served to guests. The incident occurred at only one bar, and it involved seven tourists, ranging in age from young to older, who fell ill.

“The resort management shares our concerns and is fully cooperating with the Ministry of Health and other authorities to identify what happened and to ensure the safety of all future guests.”

Gavoka went on to emphasise the safety of tourism facilities and services in Fiji, and that this was a very “isolated incident.”

Fiji police were investigating.

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Warwick Fiji confirmed that four of its guests were in hospital and said it was awaiting test results.

“Please rest assured that we are taking this matter very seriously and are currently conducting a thorough investigation.

“We do not have conclusive details but we are committed to ensuring the safety and wellbeing of our guests.”

On Monday the Labor minister Jason Clare described the “horrific” apparent alcohol poisoning as “a real terrifying sense of deja vu” after the death of two Australian teenagers in Laos.

“I guess my message for Australians travelling overseas is just be really, really careful with whatever you consume, whatever you’re drinking when you’re overseas, and please go to the Smart Traveller website to get all the information that you need.”

On Sunday afternoon Dfat updated its travel advice for Fiji to highlight a warning about the risk of alcohol poisoning.

“Be alert to the potential risks around drink spiking and methanol poisoning through consuming alcoholic drinks,” the updated advice stated. “Get urgent medical help if you suspect drink spiking.”

The suspected alcohol poisoning comes after two 19-year-old Victorian women, Bianca Jones and Holly Bowles, died from methanol poisoning in November after drinking tainted alcohol while holidaying in Vang Vieng in Laos.

– Additional reporting Agence France-Presse