A bus driver rescued a young child found wandering barefoot in cold temperatures, the Milwaukee County Transit System said.

The boy, who was less than a year old, was wearing just a nappy and onesie when driver Irena Ivic spotted him on 22 December, along her route in Milwaukee, MCTS said.

Ms Ivic stopped her bus, ran across the street, picked up the child and carried him to the bus.

As she called for help, a passenger gave up her coat to keep the boy warm before police and firefighters arrived.

Authorities say besides being cold and frightened, the toddler was OK.

Police say the child had been left outside by his mother who may have been suffering from a mental health crisis.