The dogs eventually ran into a bush area and have not been seen since.
"It is our priority to locate these dogs and officers will be conducting patrols in the area until they are found."
The area is largely residential with some lifestyle blocks and the odd area for grazing. Locals were concerned about pets and children.
The dogs were described by one witness as a tan pit-bull and a tan ridgeback.
The woman heard the attack on the alpaca and asked for locals to look out for them.
She said the animals would be easy to spot because they were covered in blood.
Anyone who sees the animals should call Auckland Council on (09) 3010101.