Victoria's Country Fire Authority (CFA) believes a number of fires that broke out near Pakenham on Melbourne's south-east fringes on Thursday afternoon may have been deliberately lit.
Twelve grassfires broke out north of Pakenham.
The fires came within 100 metres of homes before being controlled.
The CFA believes at least eight of the grassfires were deliberately lit, while the others were sparked by embers.
CFA operations officer Trevor Owen says firefighters are working with police to investigate the fires.
Meanwhile, crews have been working to extinguish another fire that started in a recycling plant in South Pakenham.
It spread to nearby grassland but was brought under control.
A fire in forest in West Gippsland south-east of Aberfeldy, near the Thomson dam was expected to burn through the night.
It has already burnt more than 1,500 hectares, and is believed to have damaged four holiday houses.
Campers and visitors were asked to leave the area.
The CFA has declared a total fire ban for Friday in Victoria's Northern country, North East, East Gippsland, West and South Gippsland districts.
Victorians are being urged to stay on alert and monitor fire updates.
Authorities are warning fires that break out will move quickly.
Meanwhile, Victorian police are searching for the driver of a dark green ute seen near a large grass fire at Little River, south-west of Melbourne, on Monday.
The blaze burnt about 1,400 hectares of farmland but detectives can not say whether the fire was deliberately lit.
The ute had a distinctive dark green canopy and was seen close to the fire.
Police are urging anyone with information to contact them.
© ABC 2013
14:24 EDT Thunderstorms are due to develop daily across New South Wales and Queensland for almost two weeks.