Concerns are held for the health of three detainees on the roof of Sydney's Villawood Detention Centre, as their protest enters its seventh day.

"They are very weak, they are very distressed, they are very disappointed," Social Justice Network advocate Jamal Daoud told AAP this morning, after speaking with the detainees on the phone.

Immigration Minister Chris Bowen, who said the men would not get the visas they were seeking, confirmed they had not eaten in days.

"Clearly now they have been up there for some time and they have not been taking food," he told reporters in Sydney.

"We are more than happy to engage with you... about your issues, of course, and provide food.

"But we don't engage with people while they are engaged with activity on the top of a roof."

Majid Parhizkar, 24, from Iran, and stateless Kurdish men Mehdi and Amir, whose applications for asylum have been twice rejected, climbed onto the roof last Wednesday.

It was the same day a riot involving up to 100 detainees broke out, leaving nine buildings gutted by fire.

A Department of Immigration and Citizenship spokeswoman confirmed the three detainees remained on the roof this morning.

"DIAC (Department of Immigration and Citizenship) officers are happy to meet with them, if they come down from the roof," she said.

She denied a claim by Mr Daoud that two men had been arrested at the centre overnight.

"There were no arrests," she added.

A spokeswoman from Serco, the private company operating the centre, also said she was unaware of any arrests.

At a press conference today, Mr Bowen announced the rooftop protesters would not get the visas they were seeking.

"The situation at Villawood is that we have people from time to time who think it is okay to protest on a roof. They won't come down until they get a permanent visa. Well they are not getting a permanent visa," he said.

Mr Bowen also dismissed reports the detainees who protested at Villawood were connected to the rioters at Christmas Island in March.

Eleven people "of interest" over those riots had been kept "under lock and key" at Villawood.

"I have heard those claims and have investigated them fully," Mr Bowen told reporters.

On Friday, 22 of the alleged Villawood rioters were taken to Sydney's Silverwater jail and Mr Bowen said they were being questioned by the Australian Federal Police.

- AAP