An alert bus driver rescued a young child wandering bare foot along a busy road in cold temperatures.

Milwaukee County Transit System (MCTS) said the lost boy, thought to be under one, was wearing just a nappy and onesie when driver Irena Ivic spotted him on December 22 along her route in Milwaukee, Wisconsin.

Transit video showed the boy walking down an overpass.

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

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