A helicopter crashed into the roof of a Hilton hotel in northeastern Australia on Monday, police said, igniting a blaze atop the building and forcing a mass evacuation.

Mangled pieces of the helicopter's propeller landed in the hotel's pool, said an emergency services official, adding that one man was treated at the scene with life-threatening injuries.

Hundreds of patrons were evacuated from the DoubleTree by Hilton, in the tropical northern city of Cairns, after the helicopter crashed around 1:50 am local time.

Images showed a bright plume of fire blazing on the hotel's roof.

"They just flew into that building," a female voice says in a video shared on social media that captured the aftermath, as sirens blare in the background.

"Madness, man. Shivers. People were living in that. It smashed right in."

Queensland Ambulance supervisor Caitlin Denning said the aircraft's propellers had "dislodged".

"One landed on the Cairns Esplanade and there was a second propeller located in the hotel pool on the bottom floor and it was on fire," she told local media.

Queensland police said "there were no injuries sustained by people on the ground".

Cairns is a popular tourist hub that offers a gateway to Australia's famed Great Barrier Reef.

A team of government investigators from the Australian Transport Safety Bureau have been dispatched to the crash site.