Refugees have left one of Australia's offshore detention centres on Sunday for the United States as part of a swap brokered by former US president Barack Obama last year.

Refugee Action Coalition's Ian Rintoul said he had spoken to some of the group by phone and that 22 men were in Port Moresby on Sunday night.

A supplied image of asylum seekers leaving the Manus Island detention centre on Sunday. Credit:AAP/Supplied by Refugee Action Coalition

Mr Rintoul said the group - including Sudanese, Afghan and Rohingya asylum seekers - had been told they would be flown to the United States via the Philippines on Wednesday.

"They're happy they're going, and they never want to hear about Australia again," he said, speaking from Sydney.