A British man being held in Sydney's Villawood Detention Centre for overstaying his visa has died, the Immigration Department says.

Police and paramedics were called to help the 29-year-old who was not breathing when staff found him in his quarters about 3.20am today.

He could not be revived and was pronounced dead, an Immigration Department spokesman said.

The man, who did not arrive in Australia by boat, had been detained for breaching his visa conditions and was due to be deported.