A 21-year-old British woman has died and a 30-year-old British man is in a critical condition after being stabbed at a backpackers' hostel in Queensland, Australia.
The attacker allegedly shouted "Allahu Akbar" - Queensland Police Service said up to 30 people witnessed the "senseless act of violence". A 46-year-old local man also suffered non life-threatening injuries.
A 29-year-old French national has been arrested.
The stabbing took place at Shelley's Backpackers accommodation in Home Hill at around 11.15pm local time on Tuesday, police said.
The hostel is in a small town - it is a popular place for backpackers to find fruit-picking work. It's about 62 miles from the coastal city of Townsville in North Queensland.
Deputy police commissioner Steve Gollschewski said the investigation is in its early stages and all motivations are being considered, including criminal and political, as well as the impact of drugs and mental health problems.
He said: "Initial inquiries indicate that comments which may be construed as being of an extremist nature were made by the alleged offender. It is alleged that the suspect used the phrase 'Allahu Akbar' during the attack and when arrested by police."
Detective Superintendent Ray Rohweder, from Queensland Police Service, said officers were confronted with a "terrible scene" when they arrived.
The woman was found dead at the scene and the British man was rushed to hospital in a critical condition. Both the victims' families have been contacted.
He said he couldn't tell reporters how long they had been in the country and whether they knew each other. But they were all staying at the same accommodation.
The 46-year-old man has been released from hospital. Police said a dog had also been fatally injured in the attack.
The man taken into custody is a visitor to Australia who has been in the country since around March on a temporary visa. He has no known local connections, Gollschewski said.
He said they were still trying to find out what he has been doing in the country since his arrival but he was not known to police before the attack.
Police aren't searching for anyone else in relation to the incident and there is no known ongoing threat to the community.
Gollschewski added: "This is not about race or religion. It is individual criminal behaviour."
The fact that the suspect shouted the phrase "Allahu Akbar" - which means God is Greatest in Arabic - had been confirmed as officers were wearing body-worn video cameras.
He is believed to have been acting alone. Police have retrieved a knife which is believed to have been the weapon.
Gollschewski said the woman was the first person to be attacked and that the incident was at the moment being treated as a murder case, not a terror attack.
Rohweder said: "Witnesses have said that they have observed the person attacking one of the persons and as a result of that there was another altercation and subsequently the male person has gone back upstairs at the accommodation complex."