The Institute of Animal Control Officers believes dangerous dogs are being hidden from councils by owners.
Three people have been seriously injured in dog attacks since Thursday, including two young girls who needed surgery after separate attacks by breeds of pitbull.
Institute president Les Dalton says some owners get around the system by registering dangerous dogs under the incorrect breed.
Mr Dalton says current laws are tough enough, but detecting dangerous or menacing dogs in order to enforce the law is the major problem.
Local Government Minister Rodney Hide is due to review dog control laws this year.
Invercargill council wants law change
Invercargill City Council wants dog control laws changed so it can put down dogs which have attacked people, even if the owner objects.
Under current laws, the council says a court order has to be obtained if a dog's owner does not consent to a dog being destroyed.
Environmental services director William Watt says the proposal was supported by most local councils at a conference of Local Government New Zealand last year.
Mr Watt says it costs $7 a day to hold each dog and they sometimes have to be held for months. In some cases, owners have broken into the pound to free their dogs during this time.
Girls recovering after attacks
A five-year-old girl attacked by two pitbull crosses on Sunday is still recovering in Waikato Hospital.
The girl underwent 10 hours of surgery after she was attacked while on a family visit to friends in Taneatua, in eastern Bay of Plenty.
A spokesperson for the hospital says the girl is now in a ward and is recovering well.
Meanwhile, a three-year-old girl from Wairoa attacked by a pitbull on Sunday has been discharged from a hospital in Hastings. She needed 23 stitches to her face.
No charges have been laid in connection with the attack.
In both cases, the dogs have been destroyed.