A FIFTH boat of asylum-seekers in a fortnight is emblematic of one of the world's biggest challenges, the Immigration Minister, Chris Evans, said yesterday.

On Wednesday, a boat of 48 asylum-seekers and four crew was spotted sailing west of Darwin. The navy boarded the boat late that night and will transfer asylum-seekers to Christmas Island, taking numbers of detained there to about 750.

Facing growing pressure over the surge in boat arrivals, the Government insisted yesterday Australia's immigration facilities on the island were coping.

The island, closer to Indonesia than to the Australian mainland, has a capacity of 1200. Surplus detainees face identity, health and security checks in Darwin, Senator Evans said.

''This will be one of the great issues of the 21st century: people movement,'' he said. ''We've seen record numbers of people moving throughout the world, record numbers of asylum-seekers, and some sort of naive belief that Australia is going to be somehow excused from facing those problems is a nonsense.''

Australia accepts less than 2 per cent of the world's refugees, United Nations figures show. The majority are resettled in developing nations closer to the countries they are fleeing.

People fleeing unrest in Sri Lanka and Afghanistan are increasingly making the voyage to Australia. Indonesia and Malaysia are the stopover points.

Yesterday, the Opposition spokeswoman on immigration, Sharman Stone, asked what the Government would do when the Darwin detention centre was full.

But the Minister for Home Affairs, Brendan O'Connor, dismissed her question as ''dog whistling''. The Coalition maintains the rise in boats is linked to the scrapping of temporary protection visas last year.