Police are warning motorists to take car after a semi-trailer carrying cattle overturned on a Tullamarine Freeway off-ramp to the Western Ring Road.
About 20 cows are on the loose.
Traffic is affected on outbound lanes of the freeway as police try to secure the animals.
Victoria Police media officer Glen Atwell said the animals were blocking two lanes as they moved along the freeway and nearby grassland.
"The cows are spooked and traumatised and police are trying to get them under control and get them off the road," he said.
It is not known whether the driver of the semi-trailer was injured, and the cause of the crash is also unknown.
Another police spokesman said motorists were still travelling at high speeds in the area and urged them to slow down.
"There's a lot of cattle floating around, these cattle are fairly spooked and are going to be quite unpredictable,'' he said.
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