Auckland Council's crackdown on unregistered, menacing dogs is bold but will not solve the problem, a dog-control officer says.
And the SPCA said it would take a long time to get dangerous dogs off the streets, and it was time the government changed dog control laws.
After a series of nasty attacks the council is giving owners who have not registered their dangerous dogs until the end of June to do so.
It will waive the registration fee and offer $25 de-sexing for those who come forward, but once the deadline has passed there will be a region-wide crackdown with officers seizing animals and fining their owners.
The animals will either be put up for adoption, if they pass a temperament test, or they will be put down.
The amnesty covers the Brazilian Fila, Dogo Argentino, Japanese Tosa and Perro de Presa Canario - along with Pit Bull Terrier-type dogs.
There are just over 3000 of them already registered in Auckland.
Auckland Council said pit bulls and their crosses were 20-times more likely than any other breed to be involved in a serious attack.
The council estimated there were 25,000 unregistered dogs across the city but it did not know how many of them were from dangerous breeds.
New Zealand Institute of Animal Control Officers president Les Dalton told Morning Report he wanted other councils to offer an amnesty even though he was not sure how effective it would be.
"I think you'd be fooling yourself if you think that by offering these sorts of amnesties that the dog attacks are going to go away. They won't because unfortunately a lot of people that own these sorts of breeds are not willing and compliant types and you have to go hunting for them, they won't voluntarily come out no matter what sort of carrot you wave under their nose."
The SPCA's Andrea Midgen said it would take animal control officers a long time to find and process unregistered dogs.
"I heard this morning they've got 46 animal management officers to cover the whole of the greater Auckland area, and it takes a lot of time to deal with each animal and each owner."
The council's amnesty also included the offer to .
Ms Midgen said the council's offer to de-sex the dogs for $25 was a good start. She is in talks with officials about continuing it past the June deadline, and applying it to all breeds unless the owner was a registered breeder.
"From a council and SPCA point of view we'll carry on a de-sexing program anyway. That may not include the amnesty around the registration, but it certainly will be focused on cheap, if not free de-sexing, going forward."
She said it was time the government stepped in.
"I'm just hoping that the government will make this a non-political issue and look at strengthening up that Dog Control Act so that this compulsory de-sexing is in place and we can stop the problem."