THE number of international students attempting to claim refugee status is likely to multiply by the middle of next year.

That is when the first batch of 18-month bridging visas runs out, according to an expert on migration and international students.

And the scenes witnessed at Villawood Detention Centre, which included five international students taking to the roofs, were "utterly predictable".

"What happened at Villawood was absolutely predictable and absolutely related to changes in how the government decided to deal with permanent residency," said Shanthi Robertson, a lecturer in the sociology of migration at RMIT University.

"But this is only the beginning. The real crunch will be in the middle of next year when those 18-month bridging visas that were granted actually finish."

The government's decision last year to delay until the end of next year the processing of permanent residency applications for international students whose occupations were not on the critical skills list left thousands in limbo.

Dr Robertson said while a lucky few would have found employment and sponsorship, others would be doing what they could to get residency, including applying for refugee status or for residency under partnership visas. "Some will be genuine because they have been studying here for a number of years and they do have genuine relationships. Others, however, may not be genuine and just a means to an end," she said.

Her comments were backed up by Sydney immigration lawyer David Bitel, who said the tougher skilled migration rules would lead to many former international students seeking refugee status.

"Regrettably, a significant number of overseas students will choose to go down that path," said Mr Bitel, a past president of the Refugee Council of Australia.

It was regrettable because many would not be refugees and fabricated claims would only make it harder for genuine cases, he said.

Dr Robertson said legal routes to permanent residency would include enrolling in courses on the critical skills list, such as nursing, and upgrading qualifications from vocational education and training to university, and from bachelors to masters and PhDs.

"The reality at the end of the 18 months is that while some will go home, others for whatever reason won't," she said.

"And some can't because they don't have the money."

Mr Bitel said officers of the Department of Immigration and Citizenship already had been challenging refugee claims by ex-students since the tougher skilled migration rules were announced.

Immigration officers were suggesting these students had lodged refugee applications only because they no longer had prospects as skilled migrants, he said.

Mr Bitel said Labor had little choice but to clean up the skilled migration mess inherited from the Howard government. But how it went about its reforms could have been "better thought through".

In particular, Labor could have allowed ex-students caught by the rule changes to continue to apply for the 886 visa for skilled migrants sponsored by relatives, he said.