He announced that 57 refugees now held in indefinite offshore detention would not be allowed to enter the country's mainland on medical grounds.
The government had warned past year that the medical-treatment law could allow all the asylum seekers on the islands to come to Australia and encourage more of the risky people-smuggling journeys.
The immigration minister can still reject transfers based on national security grounds, but these powers have been curtailed.
Morrison said the island's high-security Northwest Point Immigration Detention Center was ready to accept up to 250 men transferred for medical treatment and can be quickly ramped up to accommodate 600. "There is no change to those arrangements", he said.
"I never forget that it was my party, the Labor Party, that sent asylum seekers to Nauru and Manus nearly six years ago and the Leader of the Opposition Bill Shorten and his colleagues within the Labor Party have found it a very convenient distraction from questions about, "Well if you do win the election Mr Shorten, exactly what are you going to do about the nearly 1,000 asylum seekers left on Manus and Nauru".
"You know, a frolic to Christmas Island - what a waste of money". Boats carrying asylum seekers from Africa, the Middle East and Asia had been arriving daily from Indonesian ports, but the smuggling attempts have all but stopped since the government announced that no refugees who arrive by boat will ever be allowed to settle in Australia.
Catherine Stubberfield from the United Nations refugee agency said the long-term, arbitrary detention of asylum seekers was causing harm.
"The key question is where refugees and asylum-seekers, who have done nothing wrong, may best recover".
"Those who are now ill among them are unlikely to recover in a remote, formal detention environment such as Christmas Island", she said.
Australian Prime Minister Scott Morrison is seen inside a high care accommodation room as he tours North West Point Detention Centre on Christmas Island, Wednesday, March 6, 2019.
"It's the same sort of stunt".
Nobody has so far applied under the new medical evacuation laws, which came into effect on Saturday. After he left office, the centre-left Labor government began holding refugees on Christmas Island.
"It's not a place where people can be referred to, it's a place where you can transfer patients over to the mainland or offshore", he added.