The victim was walking on Ben Jonson Road in Stepney Green, Tower Hamlets at around 08:30hrs on Wednesday, 28 September when she passed a man with two dogs.
As she did so, one of the dogs lunged at her and bit her several times on the hand and arm.
A passing taxi driver intervened to free the victim from the dog’s grip. She was taken to hospital where she stayed for several days receiving treatment.
The owner of the dogs left the scene prior to police arrival.
Detective Inspector Luke Hampton said: “This was a shocking and sustained attack on a young girl as she walked to school.
“The incident not only left her with serious injuries – including broken bones – but has also left her traumatised.
“We need to quickly identify the owner of these dogs to make sure this does not happen again.”
Anyone with information is asked to call 101 with reference 2628/28SEP.