A controversial offshore migrant detention centre on Christmas Island is to reopen, Australian Prime Minister Scott Morrison announced Wednesday, as he doubled down on hardline policies after a historic legislative defeat.

Australia's conservative government is facing a huge electoral defeat as it heads into the final sitting of parliament ahead of a national election expected in May, a widely watched poll found on Monday.

Australia's prime minister and top colleagues campaigned over the weekend to block a bid to allow asylum seekers in offshore camps to come to Australia for medical treatment, saying tough rules on migrants should not be eased.

The Fairfax-Ipsos poll published on Monday showed Scott Morrison well ahead of his centre-left Labor opponent Bill Shorten as preferred prime minister.

Julie Bishop announced she would move to the backbench and had not yet decided whether to contest the next election, which is due by May 2019.

The proposed sale of Australia's largest cattle operation to China was "contrary to the national interest," the government said on Friday.