Immigration Minister Scott Morrison toasted his Cambodia refugee deal with champagne, but the UN, opposition and Greens have been quick to condemn it.

While Immigration Minister Scott Morrison has been toasting his Cambodian refugee deal with champagne, the United Nations and protest groups have been swift to condemn it.

The Australian Greens have called the celebration of his “dirty deal” crass and sickening, while Labor says it is a “complete farce”.

Mr Morrison signed a memorandum of understanding with Interior Minister Sar Kheng in Phnom Penh on Friday to allow refugees processed on the Pacific island of Nauru to resettle in Cambodia.

Afterwards, the pair toasted their deal with champagne.

“A number of those found to be in genuine need of protection will now have the opportunity and support to re-establish their lives free from persecution,” Mr Morrison said in a statement.

It would be up to Cambodia to determine when it accepts the refugees and how many, but the hope is to begin voluntary resettlement later this year, he said.

Nauru detainees found to be refugees could be resettled anywhere in Cambodia, with Australia providing support for housing, education and health as well as language training.

Australia will give Cambodia $40 million in extra assistance over the next four years in return.

Cambodian officials have said they might only start off with five refugees, but Mr Morrison downplayed such reports saying Phnom Penh had made a “very strong commitment”.

“What Cambodia is saying, and we agree with them, is that you have to start off small, make sure the program is working, and then build it up over time,” he told the ABC on Saturday.

But the Greens say the deal is a “fundamental failure” and a $40 million bribe to a corrupt government that will unleash human misery: celebrating such a deal was in poor taste.

“On budget night we had Joe Hockey dancing, and now we have Scott Morrison popping champagne corks after signing a dirty deal with one of the most corrupt and poorest nations on Earth,” Senator Sarah Hanson-Young told reporters on Saturday.

“It’s crass, it’s sickening.”

The minister brushed off criticism, saying the toast was standard protocol in Cambodia.

“I’m not going to disrespect my host,” Mr Morrison said.

The opposition has labelled the deal a complete farce that will see only a handful of refugees resettled.

“It is no wonder Scott Morrison refused to answer questions (at the signing),” opposition immigration spokesman Richard Marles said.

The United Nations refugee agency says it is “deeply concerned at the precedent” and has urged Australia to reconsider.

“It’s crucial that countries do not shift their refugee responsibilities elsewhere,” UN High Commissioner for Refugees Antonio Guterres said on Friday.

About 100 people protested outside the Australian embassy.

“(Cambodia) couldn’t give humanitarian support even if we wanted to … Cambodia is poor as hell,” Ou Virak, chairman of the Cambodian Centre for Human Rights, told AP.

In Australia, about 70 protesters chanting “free the refugees” and “freedom, azadi” gathered along the perimeter fence of the Brisbane Immigration Transit Centre at Pinkenba.