Crocodile snatched man, 52, from boat into croc-infested waters during family trip.

Police and park rangers were combing the dark and treacherous waters of a billabong on Saturday night for a father snatched from a fishing boat by a crocodile earlier in the day.

Northern Territory police confirmed the man, 52, was in a boat when he was attacked on a billabong at Cooinda in Kakadu National Park on Saturday afternoon.

'Look we always hold out hope but obviously a crocodile attack is very serious and there are grave concerns,' Superintendent Bob Harrison told the ABC.

It's believed the man's wife, son and daughter-in-law were with him at the time and witnessed the attack.

'I believe the son was involved in the initial search for his father, which is obviously traumatising and anyone's heart would go out to the family in that sort of incident,' Supt Harrison said.

Police and rangers are searching for the man and the crocodile.

'At this time we have eight people down there and we'll be ramping that up if we don't locate the gentleman during the night,' Supt Harrison said.

Unless people who are snatched by crocodiles are found alive within the first minutes, officials admit there is very little chance of them surviving. 

The family were being comforted by police and medical officials late last night.

Authorities are stunned by reports that the man, who has yet to be named, had been grabbed by the crocodile while he was on a boat - a situation that is usually considered safe.

It is believed the man was attacked by a salt water crocodile, one of the most feared and dangerous creatures on earth.

On Saturday night, Northern Territory Minister for Parks and Wildlife Bess Price said her thoughts were with the family and friends of the man.

She also wished good luck and safety for the police and park rangers who were determined to continue searching for the man through the night in the slight chance that he has been able to get away from the reptile and swim to a river bank.

Cooinda is a popular tourist area in the heart of the World Heritage-listed Kakadu National Park - where the original Crocodile Dundee movie was shot.

There is always a danger when we go to the territory of wild animals. Just because we see ourselves as tourist, doesn't mean they also see us that way. We are first and foremost food to them and then possibly companions. So when you get anywhere close to a wild animal, don't let your guards down, be aware of whose presence you are in the mist of. It could just save your life. Because the man in this story didn't take this simple advice, he is likely almost certainly dead.