The dog “jumped on the baby girl and bit her in the head,” a police spokesman told AFP, adding that another dog, a Jack Russell, joined in the attack, also biting her several times.
“The mother and girl couldn't do anything,” he said. “The attack was extremely violent.”
When rescue workers arrived the girl's heart had already stopped and she died on the spot, he said.
He said the Rottweiler fled and was later shot dead by a hunter alerted by police.
The Jack Russell will be put down, police said.