Boy, 12, taken by crocodile in Australia

The boy was swimming with friends in the Mudginberri Billabong in Kakadu National Park on Sunday afternoon when the group was attacked. One other boy suffered bite wounds as he tried to fight the creature off.

"It is believed the 12-year-old boy was taken by a crocodile as he and a number of other young boys were swimming in the billabong," said acting police commander Michael White.

"One other boy, also aged 12, was bitten on the arm by the crocodile and has received medical treatment from attending St John Ambulance members."

Aerial, land and boat searches in and around Magela Creek, which feeds the billabong or waterhole, continued throughout the night but there was no sign of the boy.

Searchers have been issued shoot-to-kill orders for any crocodile longer than three metres (10 feet) sighted in the area of Mudginberri Outstation, which is about 200 kilometres (124 miles) east of Darwin.

Two crocodiles were shot and cut open, but they had not ingested any human remains.

"One 4.3 metres; one 4.7 metres," Sergeant Stephen Constable said of the creatures.

"We've since had a look at both crocodiles and neither of them had anything in their stomachs."

Constable said a specialist was also examining the bite marks on the boy who escaped and "hopefully it'll give us a rough idea of how large the crocodile was."

Saltwater crocodiles can grow up to seven metres long, weigh more than a tonne, and are a common feature of Australia's tropical north.

Their numbers have increased steadily since the introduction of protection laws in 1971, with government estimates putting the population at 75,000-100,000.

The most recent fatality was in August last year, when a man was taken by a 4.7-metre croc as he swam across the Mary River.

Parks officials said the Magela Creek area was well signposted as a crocodile danger zone.

"We have big croc warning signs with croc jaws and a big thing saying 'croc risk; do not swim here, do not enter'," a spokeswoman said.

Australian researchers launched the world's first crocodile attack database, CrocBITE, last month, hoping to firm up anecdotal reports that harmful or fatal incidents are increasing.

Sunday's attack in Kakadu is the 11th fatality recorded so far this year by the CrocBITE team, which is based at Australia's Charles Darwin University.

The other crocodile-related deaths in 2014 have been in Angola, East Timor, India, Indonesia, Namibia, Papua New Guinea, South Africa, Zambia and Zimbabwe. Five have involved saltwater crocs.