A 12-year-old boy went missing after a four-meter-long crocodile grabbed him while swimming with friends in a water hole in the Kakadu National Park, in northern Australia.

The saltwater crocodile snatched the boy Sunday, at the world heritage-listed national park. One of the friends of the missing boy was also mauled by the crocodile, reported the Associated Press.

"One boy fought off the crocodile, and then the crocodile turned and took the other boy," Police Sergeant Stephen Constable told Australian Broadcasting Corp. radio.

Following the incident, police shot dead two crocodiles. But park rangers said that these crocodiles were not responsible for the attacks, reports BBC. "We've since had a look at both crocodiles and neither of them had anything in their stomachs," Constable said. "We're going to continue the search today," he added.

The missing 12-year-old is from an Aboriginal settlement of Mudginberri, west of Jabiru town that is famous for uranium mining, reports the Associated Press.

According to ranger Garry Lindner, killing of the crocodiles might not necessarily help in finding the boy, as a much bigger crocodile might be involved. "A smaller crocodile might initially be involved, but then, crocodile behaviour and feeding, bigger crocodiles become involved, so you have to cover all bases," he told ABC News Australia. "A bigger croc wins over a smaller croc, so you've got to take all of that into account when you're dealing with a situation."

Although, the police and the rangers resumed hunting for the crocodile, Monday, they said the wet season flooding made the search difficult. "The river's a kilometre wide where it's usually 200 metres across," Linder said.

Warning boards across Kakadu caution the visitors and tourists to avoid swimming in the waterways due to the crocodile danger. Crocodile numbers have shot up after protection under federal law in 1971. The population of crocodiles is densest in the Northern Territory, Kakadu National Park, a popular tourist destination.

Last August, a 26-year-old man was killed by a 4.7-meter (15.4-foot) crocodile while swimming in the Mary River, Southeast of Darwin. Prior to that, a teen sustained injuries after fighting off a crocodile in the same area.