A second young Australian tourist died in a Thai hospital on Friday, bringing the death toll related to suspected methanol poisoning during a night out in a Laos backpacker hotspot to six.
Two Danish citizens, an American and a Briton have also died after what media described as a night out in adventure town Vang Vieng.
The group of about a dozen tourists became ill after going out on November 12, according to British and Australian media.
"All Australians will be heartbroken by the tragic passing of Holly Bowles," Australia foreign minister Penny Wong said in a statement.
"Just yesterday, Holly lost her best friend, Bianca Jones."
"I know tonight all Australians will be holding both families in our hearts," the foreign minister added.
Australian officials are now pressing Laotian authorities for a full and transparent investigation into what happened.
At the Bangkok hospital where Bowles had reportedly received treatment, staff said they could not confirm she had been a patient there.
AFP has contacted Australia's embassy in Bangkok for comment.
- Backpacker trail -
Vang Vieng has been a fixture on the Southeast Asia backpacker trail since Laos' secretive communist rulers opened the country to tourism decades ago.
The town was once synonymous with backpackers behaving badly at jungle parties and has since re-branded as an eco-tourism destination.
"I heard the news but everything is normal here," Michael, a Vietnamese manager at Vangvieng Rock Backpacker Rooftop Hostel told AFP, asking to use only one name.
"The high season is about to start so we are welcoming more tourists every day."
"There are still many tourists in town, and they go partying," a receptionist at Vang Vieng Chill House Hostel told AFP.
Bowles and Jones, both aged 19 from Melbourne, became unwell while staying at Vang Vieng's Nana Backpackers Hostel last week, Australian media reported.
The women drank at the hostel's bar before they went out for the evening, the Sydney Morning Herald reported.
They failed to check out on November 13, when hostel staff rushed the pair to the hospital.
The Vietnamese manager of the Nana Backpackers Hostel has been detained for questioning, the Laos tourist police told AFP.
No charges have been made, however.
The Laos tourist police could not be reached for comment on Friday.
The Briton who died was named as Simone White, 28.
Her parents described her as a "beautiful, kind and loving daughter," according to the UK's PA news agency.
"Simone was one of a kind and had the most wonderful energy and spark for life," they said.
White was a lawyer with global law firm Squire Patton Boggs, which said she "was a talented colleague with a bright future ahead of her".
The US and Netherlands have not released details on their nationals who died.
But Casper Soetekouw, a spokesperson from the Netherlands Ministry of Foreign Affairs, said they were "aware of the serious reports from Laos" and were in contact via the Dutch honorary consul.
He added that "a Dutch woman was in hospital earlier this week", and she has "fortunately" been discharged.
Alcohol tainted with methanol is suspected to be the cause of the deaths.
Methanol is a toxic alcohol used in industrial and household products like antifreeze, photocopier fluids, de-icers, paint thinner, varnish and windshield wiper fluid.
Methanol can be added to liquor to increase its potency, but can cause blindness, liver damage and death.
On their travel advice websites for Laos, UK and Australian authorities warn their citizens to beware of methanol poisoning while consuming alcohol in Laos.
In neighbouring Thailand, at least six people died and more than 20 were hospitalised after drinking methanol-laced bootleg alcohol in August.