SYDNEY, Aug. 27 (Xinhua) -- Occupants of a boat, believed to be either illegal fishermen or asylum seekers, are on the run on Monday in the dense and crocodile infested rainforest of northern Australia, with authorities so far apprehending 15 of an unknown number of people.

A vessel was spotted on Sunday, partially submerged near the Daintree River in Australia's northeast coast, with a number of people spotted fleeing on foot which sparking a search by Australia's Border Force.

"We don't know whether these are illegal refugees or we don't know if these are fishermen who were maybe fishing illegally and have ended up in Australian waters and the boat's gone bad and they've got trapped," Cairns state MP Michael Healy said.

Local media have reported that the 15 men already detained are Vietnamese, a country from which asylum seeker boats are often detained in Australian waters before they reach land.

With an unknown number of people still missing, concerns are for their safety in what can be very dangerous area, inhabited by saltwater crocodiles and other deadly wildlife.

Jan Von Keyserlingk, who operates a tour boat in the area, told Xinhua that during the day the crocodiles are mostly lethargic and unlikely to pose too much risk, but at night anybody who enters the water could certainly become a target.

"If you're swimming in the river at night time there, you've got problems," Keyserlingk said.

He added that without help, the harsh conditions of rainforest are likely to get the better of the missing men.

"You can dehydrate pretty quickly even in winter and it makes you hungry walking up the steep hills where they are," Keyserlingk said.

"Before too long they'll get sick of the rainforest and come out, I guarantee it."