An elderly woman was killed by her sister's pit bull dog as she rode her bicycle past the house in Pathum Thani on Tuesday afternoon.

Her 41-year-old son, Thawee, said his mother had been riding a bicycle back to their house. He heard his aunt, who lives nearby, shouting out that his mother had been attacked by a dog.

He rushed outside and found his mother lying on the ground, bleeding from dog bites all over her body. He picked her up and ran, carrying her about 600 metres away from the scene of the attack and calling out for people to get help. Someone called a rescue team, he said.

Rescuers gave her first aid but she was later pronounced dead.

The dog's owner is the dead woman's sister. She said the pit bull was named Poi Kai and was usually kept in a cage. She and her daughter had raised it themselves since it was a puppy. 

Recently, Poi Kai had become disobedient and aggressive. It had previously attacked her daughter and a neighbour. She would give the dog to any agency able to take care of it, she said.

Police said the dog's owner would face charges.