Eight new fires started on Thursday, adding to 50 others across the state with two-thirds considered uncontained, as authorities braced for worsening conditions.

The hazard is set to peak from 5am on Friday, with hours of dry air, temperatures reaching into the high 30s, and 40km/h winds gusting up to 90km/h.

"The best thing people can do in these conditions is leave early," the Tasmania Fire Service warned.

"A fire under the expected conditions can move very quickly with the potential for embers starting fires up to 20km ahead.

"Even those whose homes are well prepared to defend against fire will find their property is not defendable in these conditions."

Adding to the challenge for fire crews on Friday, forecast winds mean water-bombing aircraft will be grounded.

"The weather tomorrow may see that our aerial assets that have been so vital to us over the past week or so, are not able to fly," regional chief Jeff Harper said.

"The wind conditions are so turbulent that rotary-wing and fixed-wing aircraft, it's not safe for them to fly under those conditions."

Ground crews will be stepped up to try and cover the loss of aircraft, but Mr Harper said efforts will be prioritised in terms of human safety and property defence.

They are battling a combined fire front of more than 800km and since late last month, some 64,000 hectares of land has been burned.

Several fires have the potential to threaten communities. A blaze at central Great Pine Tier could bear down on the township of Shannon and the Gell River fire southwest of Hobart - which has been burning since December 28 - could reach Geeveston.

Efforts are being made to clear fuel from around the communities. In some cases there is 40 tonne of fuel per hectare.

One house has been lost near central Miena, while residents remain on alert at Barren Tier, Tods Corner, Penstock Lagoon, Liawenee, Waddamana and Shannon.

A state-wide fire ban is in place until Monday.

The smoke hazard across the state is expected to worsen on Friday and remain for the weekend, with asthma sufferers among those being told to remain indoors.

The government will close some of the state's major national parks to reduce the first threat and increase public safety. The road to the pinnacle of Mt Wellington, overlooking Hobart, will be closed from Thursday night.

Other popular sites including Mount Field National Park, near Hobart, and Hastings Caves, south of the capital, will be closed.

"The government's priority is community and visitor safety," Premier Will Hodgman said in a statement.

Australian Associated Press