The CFA declared the start of the fire danger period from 1am yesterday, bringing into force restrictions across the two municipalities and urging residents and business to take the threat of grass fire seriously.

The municipality-specific fire danger periods are based on local conditions and take into account fuel moistures, fuel loads, grassland curing, weather and rainfall.

There is an above-average risk of grass fire this fire season. CFA southern metropolitan region operations manager Trevor Owen says the threat of grass fires for residential, commercial and industrial properties should not be underestimated.

''Simply discarding a cigarette butt into dry grass can put the community at risk."

He said businesses were not immune to the increased danger.

"In the southern metropolitan region, we have a lot of commercial and industrial properties that have grass in and around very large premises."

"We have in the past responded to factory fires caused initially by a grass fire."

Restrictions now in force in Casey and Cardinia include:

■ Fires in the open air are legally restricted when an fire danger period is declared. A written permit is required for burning off.

■ Lighting a fire in the open without a permit is a serious offence.

■ Barbecues and fires for cooking and warmth do not require a permit, but must be lit in properly constructed fireplaces (metal, stone or concrete), be three metres from other flammable material, be supervised at all times and not be used in strong winds.

■ Using an incinerator, chainsaw/lawn mower, welding/grinding equipment, vehicles that come in contact with vegetation and machinery with an internal combustion/heat engine are permitted, if guidelines are followed.

Details: 1800240667 or cfa.vic.gov.au.