“They didn’t eat. They didn’t drink. Their mobile battery is out,” he told SBS Arabic24.
The trio was arrested by NSW Police on Thursday afternoon and have since been transferred to Australian Federal Police custody.
Social Justice Network spokesman Jamal Daoud said the detainees were deeply depressed and living in constant fear of catching coronavirus.
In a statement, the Department of Home Affairs said there were no injuries to detainees or staff.
“The protest at a detention facility in Sydney has been resolved peacefully today with the assistance of the NSW Police,” a department spokeswoman said.
“The detention centre remains calm and normal operations are continuing.”
Coronavirus protest at Villawood detention centre ended by riot police
The detainees climbed on to the roof on Saturday, carrying banners pleading for their release.
"Free us from detention COVID-19 2020," one banner read. "We are humans too," read another.
Refugee Council of Australia chief executive Paul Power said many detainees were worried about cramped conditions.
“They are being held in situations where there is more than one person to a room and where people are crowded in common areas during meal times,” he said.
“The government has the option of moving people into the community on bridging visas with whatever conditions they like.
“It also has the option of community detention where they specify people live in a particular place.”
A separate group of asylum seekers and refugees have also been holding a hunger strike inside the detention centre.
Last month, one staff member at an immigration detention centre in Brisbane tested positive for coronavirus.
The Australian Border Force said exposure was limited as the individual had not worked in nearly a fortnight before testing positive.
Hundreds of criminal justice experts recently co-signed a letter calling on the Australian government to take "unprecedented" action and immediately release detainees in jails and detention centres.
Additional reporting by Ali Bahnasawy, Steven Trask, Lucy Murray.