UPDATE: A BUSHFIRE in southern Tasmania has been upgraded to emergency warning level as conditions get worse.

Unpredictable wind gusts and warm temperatures are making it difficult to contain the fire burning near Molesworth in the Derwent Valley northwest of Hobart.

Some residents were being told to leave their homes while the communities of Collinsvale, Glenlusk, Berriedale, Iron Stone Gully and Malbina are likely to be impacted later this afternoon.

The outer suburbs of Hobart are expected to be affected by smoke and embers.

A fire refuge centre has been opened at the Derwent Entertainment Centre in Hobart's outer north and residents between Molesworth and Collinsvale have been doorknocked by police advising them to evacuate.