Fears for woman missing from Qld houseboat

Grave fears are held for a woman who went missing from a houseboat in crocodile and shark-infested waters off the north Queensland coast five days ago.

Extensive sea, air and land searches have failed to uncover any sign of the 52-year-old from Melbourne, who was reported missing by her husband on Sunday morning.

The pair had been holidaying on the houseboat, which was moored at Hinchinbrook Island, off Cardwell.

Hopes of finding the woman alive are fading, police say.

"That area of wilderness we are dealing with is infested with crocodiles, sharks and other marine life," Detective Sergeant Michelle Clark told AAP.

The search has been focused around Hinchinbrook Island, with authorities scouring bushland, mangroves and surrounding waters, Det Sgt Clark said.

Specialist police divers and wildlife officers have also been involved in the search.

Efforts are expected to be reviewed on Friday.