Man dies in custody in NSW

An inmate suffering a medical condition has died in a NSW prison hospital, prompting an investigation by authorities.

David Dungay died in Long Bay Hospital, at the Long Bay correctional facility, on December 29.

Mr Dungay was receiving medical treatment for an undisclosed condition when he died, Corrective Services NSW confirmed on Thursday.

His death is not being treated as suspicious but is being investigated by police in the Corrective Services Investigations Unit.

"This is a very sad event. I extend my sympathy to Mr Dungay's family," Corrective Services NSW Assistant Commissioner James Koulouris said in a statement to AAP on Thursday.

Mr Dungay's death will also be referred to the Coroner for an inquest, as is standard for all deaths in custody.