The bill, which was passed by the Senate, will allow asylum seekers and refugees held in offshore detention centres in Nauru and Manus Island to be transferred to Australia for medical treatment.
"I think this country in 2019 is not the same nation as 2001".
But authorities on Christmas Island questioned the move to reopen the detention centre, saying their health facilities are limited and they "quite regularly" medically evacuate people because their small hospital can not handle complex treatment.
"People smugglers and their customers are the only winners from Labor's weakening of our border protection policies because ample medical treatment offshore and onshore was already available".
'He has no strength on this issue and he can not be trusted to follow through on any of the border protection measures that our government has put in place'.
His government, he said, was adopting "100 per cent" of a series of recommendations from the country's security services to further tighten efforts to prevent the arrival of migrants and asylum-seekers by sea.
Refugee advocates and lawyers had lobbied senators to back the amendments passed by the House.
"Most remarkably and outrageously, we've seen him announce the opening of Christmas Island".
Medical evacuations have become a loophole in Australia's policy of exiling asylum seekers who arrive by boat.
Sick asylum seekers often have to fight the Australian government in court for permission to be transferred to an Australian hospital.
"We just wouldn't have the capacity here to deal with people coming here for medical reasons", Shire of Christmas Island CEO David Price told national broadcaster ABC, adding they do not have the specialists to deal with serious mental health problems. "These people will need medical specialists and facilities that do not exist on Christmas Island, and the government is well aware of that". A wooden boat carrying 90 asylum seekers from Iran and Iraq ran onto rocks on Christmas Island in 2010, killing 48.
Home Affairs Minister Peter Dutton said part of the Christmas Island facilities "can be opened very quickly". It does not apply to anyone new, ' Mr Shorten said.
The estimate of 300 cases is in line with the estimate from Australian doctor Nick Martin, who was based on Nauru in 2016 and 2017 and told The Age and The Sydney Morning Herald last week that about 30 per cent of the 1,000 people on the islands would seek a transfer.
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The issue has galvanised the party and given the backbench hope, with Coalition sources saying if it causes a tightening in the polls, it may lead to panic in the Labor.
The new law only applies to the 1,000 people now on Manus Island and Nauru but Mr Morrison hedged when asked to confirm this fact on Wednesday, saying people smugglers did not care about the "nuance" of the law.