Refugees rejected by Australia will soon fly from the Pacific atoll of Nauru to be resettled in Cambodia.

A charter flight on Monday will fly the first refugees to be resettled in Phnom Penh under a bilateral agreement signed by Cambodia and Australia last September.

Immigration minister Peter Dutton's office did not specify when the first group will fly.

"The first group of volunteers is anticipated to depart for Cambodia in the near future," his office said.

The specific nationalities of the people to be sent to Cambodia were not released. Refugees from many countries, including Pakistan, Afghanistan, Iran and Sri Lanka, have tried to reach Australia in recent years.

The agreement specifies that all refugees who leave the Australia-run detention camp on Nauru must be volunteers.

The deal with Cambodia will cost the Australian government more than £5 million a year and has been condemned by human rights groups.