More interstate firefighters fly to Tas

A second wave of interstate reinforcements is due to touch down in Launceston to relieve Tasmania's exhausted firefighters.

The extra relief crews from across Australia will begin arriving on Sunday afternoon, with deputy fire chief Ian Bounds at the airport to arrange deployment, the Tasmania Fire Service said.

A watch and act warning continues along the Tasman Highway in Nunamara with Weavers Creek and Foons Road at high risk of ember attack, high smoke and falling ash.

Very thick smoke is making it difficult to monitor fires in the northwest, with almost zero visibility of the fire front from the air.

"Some (of it) is burning near properties but there is that much thick smoke it's hard to determine where the actual fire front is," a Tasmania Fire Service spokesman told AAP.

"Even when we try to do a line scan from the aircraft, it's not picking up the exact areas."

Dozens of fires are burning across the state, with one listed as watch and act and a further 15 with an advice message.

Many are burning in remote areas and pose little risk to communities.