Mystery surrounds how a helicopter was flown out of a major tourist airport without authorisation and crashed into a hotel roof, killing the pilot.
Hundreds of guests were evacuated and two people hospitalised after the "massive explosion" at Cairns' DoubleTree by Hilton in far north Queensland early on Monday.
An emergency exclusion zone was set up in the heart of the tourist hub after propellers were dislodged in the 2am crash, with one landing on the main street and another in the hotel pool.
"We saw the rotor on the ground. I wasn't far away. It could have got me," tourist Veronica Knight told AAP.
The identity of the pilot - the helicopter's sole occupant - is yet to be confirmed along with the circumstances surrounding the "unauthorised" flight.
Authorities on Monday would not confirm whether the four-seater helicopter had been stolen from Cairns airport.
However the chopper's owners Nautilus Aviation, a north Queensland charter company that runs scenic tours around Cairns, said on Monday it had not authorised a flight.
"The aircraft was moved from a general aviation hangar early this morning, and it was an unauthorised flight," Queensland Police's Acting Chief Superintendent Shane Holmes told reporters.
"We are working with a local aviation operator to understand the circumstances that led to the (chopper) becoming airborne."
The pilot died at the scene, with a forensic investigation under way to formally identify them.
Asked if the crash was deliberate, Acting Supt Holmes said: "Unknown at this stage, but we'll investigate all lines of inquiry.
"There is no further threat to the community and we believe this was an isolated incident."
Authorities did not think the helicopter was in the air for long but were unable to comment on how fast it had been travelling, its flight plan or whether the pilot had a licence.
Ms Knight described how the twin-engine chopper flew around at speed before hitting the hotel in a "massive explosion".
"It was like a fuel tank exploding," she said.
The Australian Transport Safety Bureau sent crash investigators to the scene on Monday.
"Once we do have an identity of the person involved then we'll start to looking a little bit more closely on all the things that may have contributed to what unfolded ... but it's only very early days," the bureau's chief commissioner Angus Mitchell said.
Ms Knight said she saw the helicopter fly around for about 15 minutes, twice going past her "really fast".
The Sydney tourist said she had never seen a helicopter travel so quickly.
"It came back real fast then went into the hotel. I was very scared," she said.
"It was like an army helicopter but faster. Like a warplane, like it was going to come in and bomb you."
Up to 400 people were evacuated from the hotel and taken to another venue in Cairns' city centre after the crash.
Two hotel guests, a man in his 80s and a woman in her 70s, were taken to Cairns Hospital in a stable condition for smoke inhalation.
"I do believe they were asleep at the time and there were some windows that may have been impacted as a result of the incident occurring," Acting Supt Holmes said.
"I think it's by pure luck that no one else was injured. It could have been worse."
Police declared a Public Safety Preservation Act, an exclusion zone.
A fire prevented emergency crews entering the hotel immediately.
DoubleTree by Hilton management said all guests and staff were safely evacuated from the premises.
"We are actively arranging alternate accommodations for these guests for this evening," a statement said.
Queensland Premier Steven Miles described it as a "terrifying event".
"I can't imagine how scary it would be to be asleep and to hear that bang and to have to be evacuated."
