Ambulance crews were called to Newhaven after a baby boy started choking.
The youngster was on a bus between Acacia Road and Denton Rise.
The Herald understand the driver of the bus came to the baby’s aid before the ambulance arrived.
A spokesman for South East Coast Ambulance Service said “We were called to a Compass Bus at the junction of Acacia Road and Denton Rise at 9.20am to reports of a baby boy with breathing difficulties.
“An ambulance car was on the scene within a couple of minutes then was joined by an ambulance crew.
“The baby was taken to the Royal Alexandra Children’s Hospital.
“We are always extremely grateful when anyone helps to resuscitate patients prior to our arrival.”