A health alert has been issued in Tasmania due to thick smoke from bushfires, as local communities could be impacted for weeks to come.

Tasmanian health authorities are urging people with health conditions to leave their homes as dense smoke blankets Hobart from bushfires burning in the state.

State Public Health Director Mark Veitch warns that smoke levels at Cygnet, south of the capital, and surrounding areas, could cause serious health issues, and that residents should minimise exposure.