Emergency crews were called to the Joseph Street unit at Rokeby on Thursday morning.

Nobody was home at the time and the fire caused about $150,000 damage.

Fire investigators were at the scene and police are now involved.

Anyone with information in relation to the fire, or who saw or heard suspicious activity in the area around the time, is asked to contact Tasmania Police on 131 444 or Crime Stoppers anonymously on 1800 333 000.

Information can also be provided online at crimestopperstas.com.au