The Valley's air was the worst affected by fuel reduction burns conducted across Victoria, according to Environment Protection Authority air quality and particle level data.

Plumes of smoke also crossed the Bass Strait and shrouded Tasmania, impacting the island's air quality.

Smoke began to cover the Valley on Wednesday after burns were ignited throughout Gippsland and the state on Monday and Tuesday.

By about 1am visibility had dropped and by 3am the air quality was classified very poor, the authority's lowest indicator.

The Valley's fine particle levels peaked almost 14 times higher than most of Victoria between 4am and 5am Wednesday morning.

Visibility was very poor on Thursday and Friday.

While health providers and the hospital did not treat any smoke-affected patients, the authority warns fine particles in the air can impact on health.

``These fine particles can get into your eyes and respiratory system where they can cause health effects such as burning eyes, sore throat and runny nose,'' the authority's website said.

``People that have existing respiratory or heart conditions...are more sensitive to the effects of smoke.''

Bureau of Meteorology Sale duty forecaster Don Whitford said northwesterly winds would have picked up yesterday and begun to clear some of the smoke.

But he said on Thursday visibility was down to about 6km in Sale.

On a fine day visibility would be about 25km.

He said weather conditions in the Valley meant smoke generally settled at night and the light winds of the past few days were not strong enough to dissipate it.

``Generally, but not always, with light winds the smoke won't disperse vertically into the atmosphere and as the cooler air slides down the valleys overnight it tends to concentrate the smoke,'' Mr Whitford said.

``That tends to keep the smoke haze close to the ground.''