The conservative government has taken a tough line to stop the flow of boatpeople since coming to power in September 2013, turning back vessels when possible in military-led operations. Those that do arrive on land are denied permanent settlement in Australia.

Immigration Minister Peter Dutton said that last month marked one year since a boat carrying asylum seekers had successfully arrived in Australia, with 20 turned back.

"We have had 633 people that would have arrived otherwise on those ventures," he said.

A Vietnamese boat was the latest known attempt, with 46 Vietnamese asylum seekers intercepted and sent home last month. The boat was reportedly sighted by an oil tanker around 149 kilometres (93 miles) offshore of Dampier in the state of Western Australia in late July, with the government refusing to comment at the time, citing operational security.

"There were 46 people on a recent venture that did come from Vietnam and we have negotiated their return to Vietnam," Dutton told reporters without saying when they were sent back to the Southeast Asia nation. He also did not reveal what happened to them after they were returned home, only noting that they "arrived back safely".

"We have worked on a bilateral basis with the Vietnamese government... The boat that they came on has been scuttled and we have been able to stare down that venture and it's a significant outcome," he said.

Dutton added that the return of asylum seekers was negotiated "on a case-by-case basis" with Vietnamese authorities.

- AFP