Twenty-nine houses have been destroyed in the bushfire that started in Bunyip state forest last week, authorities have confirmed.

Two more houses were destroyed at a separate fire at Yinnar South.

Both the fires were started by lightning strikes in bushland in west Gippsland.

A spokeswoman from the Country Fire Authority said that rapid response teams had inspected more than 447 properties to date, and discovered the 29 destroyed houses as well as two more that were damaged but habitable.

A number of sheds and other infrastructure was also lost, with 67 outbuildings marked as destroyed.

Residents who were forced to leave on Sunday when the fire began rapidly spreading toward the small town of Bunyip, about 65km east of Melbourne, were allowed to begin returning home on Thursday.

The fire, which started last Friday, has burned through 15,000 hectares and is still not fully contained. A watch and act alert remains in place for the communities of Beenack, Gentle Annie, Tonimbuk and Tynong North.

Firefighters are planning to take advantage of the cooler weather over the weekend to conduct a backburn to help contain the blaze, which authorities have said is likely to increase smoke levels.

There was a statewide air quality alert in place on Friday due to smoke from more than 20 fires that were still burning.

Smoke levels were particularly bad in north-east Victoria, with people prone to respiratory conditions around the towns of Myrtleford, Bright, Wangaratta and Whitfield advised to avoid heavy physical activity and stay indoors if possible.

More than 2,000 firefighters, supported by 61 aircraft, have been deployed statewide.

Earlier this week the Andrews government was forced to defend its decision not to conduct more prescribed burns in Gippsland, saying that fire conditions were so bad that a fuel reduction burn would not have reduced the intensity of the blaze.