The council's animal control officers have seized the pit bull which attacked the trio as well as a second pit bull, which was not registered.
The property where the dogs were kept was fully fenced, the spokesperson said.
St John ambulance team manager Norm Ngatai said they received a call about 4.30pm that a dog had attacked three people.
Two ambulances were sent to the address "because of the multiple patients and potential severity" of the injuries, he said.
He said three people were injured - two with serious injuries and one with moderate injuries.
Mr Ngatai said the dog involved was a pit bull.
Police were also called the scene and were armed.
A woman sitting in her car on Neil Rd said she was "deeply upset" by the event and it was a "tragedy" she found very distressing.
The woman said her son, sitting in the passenger seat, was a witness to the event and "saved" one of the victims, but would not say more.
The woman's son looked like he was aged in his teens.
A Neil Rd resident told the Rotorua Daily Post two dogs, one that looked like a pit bull, appeared at his house last Sunday.
He said he immediately grabbed an axe, went outside and chased the dogs away.
"I was just doing the dishes and saw them coming up the driveway so I grabbed my axe. The only reason I bolted out the door was because it was a pitty."
The resident, who didn't want to be named, said he personally wasn't afraid to take such action but it was a worry for residents in the area, particularly as there were a lot of children who lived nearby.
"The are are tonnes of kids in our street and many of them play around the railway tracks across the road."
