Australian government faces defeat as asylum seeker bill passes

Australian MPs have passed a landmark bill with an opposition amendment making it easier for sick refugees held offshore to be treated in the country.

Labor, the Greens and the crossbench combined to pass laws for the medical transfer of asylum seekers to Australia for treatment.

This is the first time in decades a government has lost a vote on its own legislation in the lower house.

The move is a blow for PM Scott Morrison's minority government's highly controversial immigration policy.

Facing certain defeat, the Coalition went to the barricades at the very last minute and furnished legal advice claiming the legislation was unconstitutional.

But Labor and the minor parties were unperturbed, pointing to ambiguities in the advice from Solicitor-General Stephen Donaghue, QC, and pushed ahead with the vote, which passed by 75 votes to 74.

Since 2013, Australia has sent asylum seekers arriving by boat to detention centers on Nauru and Papua New Guinea.

Critics say it has harmed the welfare of detainees, including children.

Doctors have long warned of inadequate medical facilities on the islands, while the UN has previously described the camp conditions as "inhumane".

However, Morrison said: "There is no form of this bill that does not weaken our border protection."

Australia has long defended its offshore detention policy by arguing that it stops deaths at sea and disrupts the trade of people smuggling.

The defeat will not trigger an early election because it was not deemed a confidence vote.

To become law, the changes must first be rubber stamped by the Senate where they originated, which should happen this week. Morrison said he would not stop them going to the Governor General for royal assent.