While spraying with pesticides is under way, the Vic Department of Primary Industries says the locusts are in plague proportions and could cause millions of dollars damage to crops.

Gordon Slater, the incident controller at the department's Locust Control Centre, said it was inevitable that the juvenile locusts would survive to adulthood and spread wherever the air jet stream took them.

"It's certainly the largest area we have had locusts involved in since the 1970s," Mr Slater said.

"We're talking several hundred locusts per square metre on the ground."

Mr Salter said young locusts were dying out in drier Victorian regions, but thriving in green areas around Dookie, east of Shepparton.

"The public will become aware over the next few weeks as they become airborne and splatter on your windscreen and start flying into your garden," he said.

"They basically work as a single organism moving across the landscape, devouring whatever green feed they can get in front of them."

Locusts can travel more more than 500 kilometres in a night and a swarm covering a square kilometre can eat up to 10 tonnes of vegetation in a day.

Premier John Brumby said earlier this week the state was doing everything it could, working with the Australian Plague Locust Commission.

"The trick with locusts is to get in early, to spray and poison them early, before they breed and become a major problem over the January period," he said.