An investigation is underway after a man died while in police custody overnight.

The 29-year-old man from Glenorchy was arrested after several reports he was acting in a suspicious and erratic matter in the Moonah area.

He was taken into custody near Main Road, Moonah about 1:55am and transported to the Hobart Reception Prison.

Medical assistance was requested about 2:30am, when he was found to be unresponsive.

Sadly, he died a short time later.

Police will prepare a report for the Coroner, who will investigate the circumstances of the death.

A Professional Standards investigation is underway and the Integrity Commission has also been notified.