A 40-year-old man from New South Wales is missing and presumed dead after falling into the crocodile-infested Annan River near Cooktown, Queensland, while fishing with his family.

The incident, described as a 'fatal attack' by wildlife officials, occurred on Saturday afternoon.

Witnesses reported that the steep bank where the man was fishing collapsed, sending him into the river.

After falling into the water, the man did not resurface, prompting a search operation that has now entered its third day.

Rangers, along with police and SES volunteers, have been conducting extensive searches for the missing man.

Authorities believe they have found human remains belonging to the missing man inside a euthanised crocodile.

A large crocodile, believed to be responsible for the attack, was euthanised by Queensland authorities.

Queensland Police confirmed the discovery of the remains after the crocodile was humanely killed.

Formal identification of the remains is currently underway, and the search and rescue operation has been suspended.

This incident marks the second fatal crocodile attack in Australia within a month, following the death of a 12-year-old girl in July.

Crocodile expert Brandon Sideleau warned that illegal feeding of crocodiles can lead to dangerous associations between humans and food.

Feeding wildlife in Queensland is illegal and can result in fines of nearly 6,500 Australian dollars ($4,200).