A woman is feared to be dead after being attacked by a crocodile during a late-night swim with a friend in Australia's Daintree National Park.

Cindy Waldron, 46, who was from Lithgow, New South Wales, was reportedly swimming in waist-deep water with a friend on Sunday night at Thornton Beach north of Cairns in Queensland when she was attacked.

"It's certainly very, very concerning at this stage and we would hold grave fears for the welfare of the woman," senior police spokesman Russell Parker told ABC.

According to the police, Waldron's 47-year-old friend tried to grab her and drag her to safety, but failed to do so. The woman ran to a nearby business and alerted the people about the incident.

Neil Noble from the Queensland state ambulance service told ABC that a 5-meter crocodile had been spotted in the area recently. Noble said that according to the surviving woman, they felt a nudge and her companion started to scream and was dragged into the water.

"The whole of Cairns and up into the Cape is known for its large crocodiles," Noble said.

Thornton Beach is known as a crocodile habitat. Police said that the women were obviously unaware of the dangers as they were not locals.

But Warren Entsch, local Queensland representative, told The Independent that the women must have seen several crocodile warning signs in the region.

"You can't legislate against human stupidity. If you go swimming at 10 o'clock at night, you're going to get consumed," he added.

A rescue helicopter using thermal imaging equipment was sent to the area but failed to find any trace of Waldron. There are also land-based and boat rescue teams in the area.

The victim's friend suffered from shock and a graze on her arm, which was said to be from the crocodile. She was taken to a hospital in Mossman.

According to AFP news agency, crocodiles are common in the northern part of Australia, and these crocodiles kill about two people on average every year. In 2014, four people were killed by saltwater crocodiles in the Northern Territory, which is the highest number of crocodile-related deaths since 1974, bringing the total casualties to 21.

According to experts, most of these deaths were due to negligence in crocodile-infested waters. Other reasons are that residents have become complacent about their safety and that crocodile population is continuously rising after crocodile hunting was banned in 1971.