More than 60 asylum seekers have been reported missing off the Australian coast, and authorities hold "grave fears" for their safety, an official has said.

The 67 people left Indonesia in a rickety boat bound for Australia more than a month ago, Jason Clare, the Australian home minister, said on Tuesday.

The news comes as the Australian government debates a tough new bill aimed at deterring the flood of asylum seekers making the dangerous sea journey.

Australian Customs and Border Protection Service were alerted over the weekend that the 67 had not been heard from since they told relatives that they would embark on the 400km voyage to the Australian Indian Ocean territory of Christmas Island in late June or early July, Clare said.

Customs had since checked a list of names of the missing against a record of the hundreds of asylum seekers who had reached the island in recent weeks.

"There is no evidence that those people have arrived in Australia," Clare told reporters. "So we now have very grave fears for the safety of those people."

Earlier in June, more than 90 asylum seekers are believed to have drowned when two people smuggling boats capsized in the space of a week while attempting the same journey in rough seas.

Another 240 were rescued and taken to a detention centre on Christmas Island.

New asylum law

Australia's centre-left Labor Party government plans to deter future arrivals by deporting new asylum seekers who arrive by boat to the Pacific atoll of Nauru or to Australia's nearest neighbour, Papua New Guinea.

They would be held in tent camps for as long as they would have spent in refugee camps if they had not paid people smugglers to take them to Australia, the party said.

The plan came a step closer to reality when Tony Abbott, the conservative opposition leader, announced that his coalition would support enabling legislation when it goes to a vote in parliament on Tuesday.

His support ensures that the legislation can pass the senate this week without the votes of the Greens party, a key government ally, which has condemned the deportation of would-be refugees as cruel.

Clare said a temporary detention camp on Nauru, established by a previous administration and scrapped in 2008 when Labor first came to power, would be opened "within weeks rather than months".

The camp at Papua New Guinea, which Labor also scrapped in 2008 because it was regarded as cruel and a waste of money, would be opened "as soon as possible", he said.

A surge in boat arrivals and the deaths of more than 600 asylum seekers at sea in the past three years has promoted a tougher government attitude.

More than 7,600 asylum seekers - many from war-torn countries, including Afghanistan, Iraq and Sri Lanka - have reached Christmas Island in more than 100 boats so far this year.

Nauru President Sprent Dabwido said in a statement he is committed to working with Australia to process asylum seekers as soon as it's practicable. Australia also has to negotiate an agreement with Papua New Guinea.

"Within a month we would hope to see people processed on Nauru and Papua New Guinea," Julia Gillard, the Australian prime minister, said on Tuesday, adding that she had spoken to the leaders of both nations and they responded positively to the idea.