Fire crews are constructing control lines around a large grassfire north of Melbourne ahead of potentially dangerous conditions.
The blaze at Flowerdale, about 90 minutes from the CBD, has increased to 800 hectares since it started burning on Tuesday.
No homes have been lost and it's understood no other structures like sheds or fences have been damaged.
The grassfire is believed to have started on a private property, the Country Fire Authority says.
On Wednesday, a 71-year-old Flowerdale man was arrested by investigators probing the cause of the fire and released pending further inquiries.
More than 100 firefighters were at the fireground on Thursday, doing back-burning works and creating 17 kilometres of control lines.
Residents are being warned smoke will be visible for days all the way to Glenburn, Kinglake and Whittlesea as firefighters focus on the southeastern section of the fire.
A watch-and-act message was still out for Flowerdale and the surrounding area on Thursday afternoon, with residents told to monitor conditions and be prepared to act.
The area will be under a high fire danger rating on Friday, with forecast strong northerly winds and temperatures in the low 30s.
On the other side of the state, a total fire ban has been declared for the Wimmera and southwest regions.
Residents in those areas will not be allowed to light any fire in the open air until 11.59pm on Friday.
"Tomorrow's conditions could make it difficult for firefighters to suppress a fire should one start," CFA chief officer Jason Heffernan said.
"There is heightened fire activity across the state ... and we're asking the community to do its part in preventing further fires from starting."
