A COVID-19 outbreak at a Sydney detention facility for refugees and asylum seekers is growing as staff dwindle due to isolation.

Australian Border Force confirmed the outbreak in Villawood Immigration Detention Centre had reached six on Tuesday.

But a refugee advocacy group says they know of at least eight positive cases and with many still awaiting results, COVID-19 cases within the compound are expected to rise in the coming days.

ABF said contact tracing, quarantining, testing and cleaning were being implemented to curb the spread in the Sydney facility.

Refugee Action Coalition's Ian Rintoul said the detention centre was a "disaster waiting to happen" following last year's outbreak in Melbourne's Park Hotel.

Nearly half the detainees held in the Melbourne detention hotel became infected with the virus in October, with at least one being treated in hospital.

Mr Rintoul told AAP up to 85 per cent of staff at Villawood were considered close contacts or had contracted COVID-19 and were isolating.

"The staff shortages magnify the risk that the Villawood outbreak cannot be safely managed," he said.

"Despite previous COVID scares at Villawood the government has done nothing to safeguard the health and welfare of detainees.

"Vulnerable detainees should have been released long ago."

A vaccination program was rolled out from early August 2021 and had been offered to all those consenting, according to the ABF.

Some 59 per cent of all detainees at Villawood have received two doses of the COVID-19 vaccine, while a further three per cent have received their first dose, as of Sunday.

The ABF said it was following preventative measures in accordance with Australian health guidelines and would continue to provide opportunities to educate detainees about COVID-19 vaccinations.