Dozens of foreigners were believed to be on the run on Monday in an Australian mangrove rainforest after their suspected illegal fishing boat ran aground in crocodile-infested waters.
The Australian Border Force said a "number of potential unlawful non-citizens" were located, but did not reveal their country of origin or whether they were fishermen or asylum-seekers.
Locals they saw people fleeing into the forest after their vessel ran aground near Daintree River in the tropical far north of Queensland state on Sunday.
Media reports said they may be from Vietnam, although a marine rescue official told broadcaster ABC it was an Indonesian boat.
Queensland Police Minister Mark Ryan told the Australian Broadcasting Corporation 15 people had been detained so far. Brisbane's Courier Mail
said up to 20 others may still be within the dense terrain.
The ancient Daintree rainforest -- some 120 kilometres north of popular tourist city Cairns -- is home to crocodiles, snakes and the giant cassowary flightless bird, one of the world's deadliest due to its aggressiveness.
State Emergency Service area controller Peter Rinaudo said his crews were searching through the mangroves and near the mouth of the river.
"It'll be a hard slog, it's still quite warm in there and it'll be tough conditions for the guys," he told national broadcaster ABC.
"I hope the people, however many there are, get located -- it's not a nice area for them to be in."
Former Border Force chief Roman Quaedvlieg tweeted on Monday that Vietnamese fishing boats "have been illegally fishing in fleets" off the far north Queensland coast in the past two years due to their own depleted fishing stocks.
"Possible the Daintree vessel & crew have used this activity as a staging point to make Oz landfall & avoid returning to VN (Vietnam)," he added.
If the boat were carrying asylum-seekers, it would be the first time in four years that such a vessel has reached Australian shores.
Asylum-seekers who try to reach Australia by boat are either turned back or sent to remote Pacific camps where conditions have been widely criticised.
They are blocked from resettling in Australia.