Revealing some of their closely-guarded methods, the smugglers said they used secret compartments such as ice boxes to take asylum seekers to Australian waters and then issue distress calls in the hope that rescue boats pick them up and take them to Australian detention centres.

Precarious situation

But even if the asylum seekers survive the often treacherous journey, their situation can continue to be precarious.

People trafficking:

 Difficult to quantify the business because syndicates' reach is global

 Amnesty International estimates trade involves 4 million people a year, valued at $10bn and growing

 Interpol says weak laws, huge profits and low risk of being caught are incentives

 Stricter asylum requirements in certain countries lead to greater demand

 UN says thousands of people killed due to indifferent or deliberate actions by smugglers

In the Christmas Island riots on Saturday, about 150 detainees are believed to have used billiard cues, tree branches and broom handles in brawls that left 37 people requiring medical treatment, including some guards trying to break up the fighting.

Australian police and the immigration department are investigating the incident, but Chris Evans, the Australian immigration minister, rejected suggestions the brawl was caused by tensions arising from overcrowding.

Evans, who said those believed to have been behind the brawl had been placed in "stronger" detention, played down the incident and blamed anxiety caused by the repatriation of some Sri Lankans for the violence.

"We've had some people removed back to Sri Lanka found not be refugees," he told ABC Radio on Monday.

"Essentially we've had a fight between some detainees which got out of hand."

The rioting comes as Australia is seeing the biggest stream of asylum seekers in seven years, a surge the government blames on the conflicts in Afghanistan and Iraq, as well as the end of Sri Lanka's decades-long civil war.

While the Labor government dismantled tough immigration and asylum laws after its 2007 election win, closing down detention centres in small Pacific island countries and saying that detention would only be used for security, it has increased ships and aircraft patrolling the remote north coast to intercept boats before they reach Australian soil.

It also continues processing asylum seekers at the Christmas Island detention centre, where the government has boosted capacity by hundreds of beds.

The centre, which can now hold about 1,200 people, is at near capacity, however, with about 1,000 people being held in facilities that were originally intended for only 400.