"The matter has been referred for investigation by appropriate agencies, including the NSW Coroner."
A detainee in Villawood said the death has triggered chaos in the centre, with detainees confronting officers.
Video posted on Facebook purportedly from within the centre shows officers trying to contain a group of detainees.
The deceased male detainee is believed to be from an African nation. He was detained in Mitchell compound, where the death is believed to have occurred shortly before 6.30pm Friday.
NSW Police said preliminary investigation suggested the death was not suspicious.
Detainees in the centre have claimed the male detainee took his own life after receiving a visit from Border Force officials who told him he would be returned to his home country.
Refugee Action Coalition Ian Rintoul said the detainee's death was "unnecessary".
"This is a completely shocking and unnecessary death; the responsibility for which lies with the Minister. It was the Minister for Immigration and Home Affairs who was keeping him in detention. The responsibility for his death lies with the Minister," he said.
Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14, Suicide Call Back Service on 1300 659 467 and Kids Helpline on 1800 55 1800 (up to age 25). More information about mental health is available at Beyond Blue.