By Phil Mercer BBC Sydney correspondent

Australia now uses its navy to hunt for illegal immigrants

They are the first boat people to have been stopped in Australian waters since December 2001.

They were detained by customs officers and will be transferred to Christmas Island to have their asylum claims processed.

A spokeswoman for the Immigration Department said she believed the boat was not part of a fresh wave of asylum seekers heading to Australia.

'Major failure'

The vessel, a fishing boat, was carrying about 50 men, women and children along with a baby.

The refugees' rickety boats often do not last the course

It's believed it had sailed within a few kilometres of the coast near the town of Port Hedland before it was spotted, having breached Australia's border security.

Immigration officials have said they did know the boat was on its way from Indonesia but had somehow lost track of it.

An internal review will try to find out why.

Opposition politicians have described it as a "major failure in coastal surveillance".

The Immigration Minister, Philip Ruddock, has refused to blame the navy or the coastguard.

He said it was often difficult to detect small boats in a "very large ocean".

He also played downs suggestions that Indonesia, with whom Australia signed a deal in 1999 to try to prevent illegal migration, had failed to intercept the boat.

"I think it has to be seen as an isolated incident and certainly not a lack of cooperation on Indonesia's part," said Mr Ruddock.

"They've been very supportive of our regional efforts to combat people smuggling," he added.

'Immigration' island

These are the first asylum seekers to have made it so close to Australia for 18 months.

Human rights groups accuse Australia of being heavy-handed

The group will be taken to a detention centre on Christmas Island.

This remote territory in the Indian Ocean - about 1,800 kilometres from western Australia - is part of a special immigration zone where those seeking asylum have fewer rights to apply for visas than on the mainland.

It also includes the Ashmore and Cartier Islands in the Timor Sea, where many boatpeople have landed in the past.

These measures were designed to deter those planning to make the hazardous journey to Australia from Indonesia.

At least two other vessels carrying Vietnamese asylum-seekers have attempted the crossing in recent months.

They were forced to abandon their trip when their boats threatened to sink.