Sick refugees and asylum seekers on Nauru cannot be evacuated to Australia for treatment if medical assessments are done remotely, under new laws passed by the island nation.

Prime Minister Scott Morrison said he was unsure what effect the changes might have on Australia’s new transfer system.

“It’s not quite clear what they’ve done and how that will play out,” Mr Morrison told 3AW on Tuesday.

“What’s happened in Nauru is a good example of what happens and how Labor didn’t think through what playing around with border protection laws will do.”

It comes after the Department of Home Affairs confirmed the Christmas Island detention centre was being reopened to move people there if they qualify for medical evacuation, rather than to the Australian mainland.

The Greens and independent MP Kerryn Phelps say that has the potential to undermine the will of the Parliament, which passed the medevac bill last week in a historic defeat of the Government.

“This is a subversion of our entire model of representative democracy,” Dr Phelps said on Twitter.

The Parliament, through its proper processes, clearly determined that people too sick to receive treatment in offshore detention should come to Australia, not Christmas Island, for specialised treatment.”

Home Affairs secretary Mike Pezzullo revealed the detail in Senate estimates on Monday night, under questioning from Greens immigration spokesperson Nick McKim.

“Is it the intention, when people are transferred back to Australia under the provisions of the amendments that passed through the Parliament last week, that they be transferred to Christmas Island?” Senator McKim asked.

“Yes. That is the policy of the Government,” Mr Pezzullo said. “But clearly, Senator McKim, it goes without saying that if a specialist is available only on the mainland, then the mainland will, of course, be utilised.”

He clarified that patients would be evacuated to Christmas Island in the first instance. The department would work to make treatment available there.

Mr Pezzullo said Home Affairs began considering the contingency plan in December when the Senate passed the bill, ahead of Labor’s amendments that passed both houses last week.

Greens MP Adam Bandt accused the Coalition of “defying the will of the Parliament” and said he would not hesitate to back a no-confidence motion.

“The conservatives are so bereft of humanity and respect for the rule of law that they have lost the right to govern. I will support any ‘no confidence’ motion moved against this train wreck of a govt. Kick this mob out,” he tweeted.

Opposition Leader Bill Shorten said Labor would be “fine” with treating refugees and asylum seekers on Christmas Island instead of the mainland.

The Australian Human Rights Commission has found that Christmas Island’s remoteness and limited access to services means it is “not an appropriate facility for immigration detention”.

Under the laws passed by Parliament last week, two doctors can recommend a refugee or asylum seeker be transferred to Australia for medical reasons.

The home affairs minister will have 72 hours to review the recommendation and consider security risks and serious criminal history.

A government-appointed medical panel can overrule the minister if there are no security risks.

Home Affairs Minister Peter Dutton insists the move might restart boat arrivals, though the new law applies only to those already on Nauru and Papua New Guinea.

The department said 431 people remained on Nauru on Monday, while there were 584 in Papua New Guinea. Most of them have been found to be refugees.