A luxury yacht with a price tag in the multimillions is a charred mess after a fire at a Perth boat ramp.

The 15m twin engine vessel was destroyed in the inferno at Hillarys Boat Ramp at 11am.

Multiple calls were made to triple zero as boaties used nearby hoses in an attempt to douse the flames.

Eight emergency services crews arrived at the scene and took over the firefighting effort.

The thick black smoke was seen billowing from suburbs away and attracted an audience.

"We were coming down from Scarborough and we thought we'd swing by to have a look, see what it was," one member of the public told 9News.

"You could see it from our house, so we came down to see what's going on," another bystander said.

Authorities said the owner of the luxury vessel, who wasn't onboard at the

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