Richard Kerbaj – Hundreds of protesters, including four Papuan refugees, yesterday rallied against the Howard Government's proposed migration bill that would lock asylum-seekers in offshore detention centres.

The four refugees, who joined more than 300 protesters outside the Melbourne Museum, were among the 42 Papuans who fled to Australia from Indonesia by boat in January and were eventually granted temporary protection visas by the Immigration Department.

Angry protesters attacked the bill and called for Immigration Minister Amanda Vanstone to be "locked up". Speaking through a translator, the four refugees told The Australian they opposed the bill and welcomed the protest.

Immigration lawyer David Manne, who represents the Papuans, told the crowd that the Migration Amendment Bill would violate Australia's legal international obligations.

"These amendments are far more radical than anything that we've seen before," he later told The Australian. "Australia's very commitment to the protection of vulnerable people in need is at stake."

The Migration Amendments Bill was introduced after Indonesia reacted angrily to the decision to grant protection visas to the Papuans in March. The bill proposes all asylum-seekers arriving by boat be processed in offshore centres such as Nauru. Presently, asylum-seekers who make it to Australia are processed in mainland detention centres.

The proposed laws have sparked division in the federal Government, with Liberal backbencher Judi Moylan reserving her right to vote against the bill or abstain during a Coalition partyroom meeting.

Democrats leader senator Lyn Allison told protesters the bill would bring disgrace and shame to Australian citizens. She said the bill would allow the Government to "completely avoid any obligation to even consider taking people who are refugees who arrive here".

Senator Allison said some refugees were suffering from health problems such as mental illnesses as a result of their detainment. "Mental illness is so common for people being held in year after year," she said.

The Australian Democrats leader praised the protesters for opposing the proposed laws, saying: "The cruel treatment of people who seek asylum in this country brings shame upon us all."

An inquiry into the bill by the Senate Legal and Constitutional Affairs Committee last week revealed the bill's "broad incompatibility with the rule of law" and its potential to breach Australia's obligations under international law if it were to be pushed through.