Rangers fear dogs are being dumped by owners trying to avoid being caught breeding or importing the dangerous animals.
The Victorian Government's Dob in a Dangerous Dog hotline has received tip-offs for 125 pit bull and pit bull crosses in its first week.
Pit bull owners have until September 29 to place their dogs on a restricted breed register. Unregistered dogs found from September 30 will be put down.
Animal welfare patrols may be introduced as part of the crackdown after Ayen Chol, 4, was savaged to death in her family's St Albans home on August 17.
Hume Council yesterday confirmed it had caught and destroyed four pit bulls "wandering at large" since last Thursday.
Agriculture Minister Peter Walsh said the changes made last week to tighten laws around ownership of restricted breeds were already having an impact.
"People are starting to think twice about the risk of owning a pit bull," he said.
Geelong Animal Aid manager Robyn Stewart has put down six pit bulls in the past two weeks and suspects the number will rise as the amnesty draws to an end.
Lost Dogs Home spokeswoman Sue Conroy said there had been a surge in the number of aggressive dogs being surrendered.
Six had been destroyed at the shelter in the past fortnight and the fate of 11 others was being decided by the council.
"People need to get some sound information on the dog. Get expert advice on whether it needs boundaries or could benefit from a little training," she said.