Parents are being warned about the danger of button batteries, which come in some Christmas toys and can be easily swallowed
An Australian coroner recommended manufacturers of the batteries make them safe if swallowed, after a four-year-old girl in Queensland died from stomach bleeding after swallowing one in 2013.
The lithium batteries can start burning through soft tissue in about two hours.
Dr Leo Schep from the National Poisons Centre at the University of Otago said the centre got calls from parents whose children had accidentally swallowed batteries.
He said it was easy for children to pick batteries and put them in their mouth.
"When they are exploring the world, not just with their hands and their eyes, but with their mouths as well, they put things in their mouth sand swallow it. So parents should be aware of that and leave no batteries lying around the place and dispose of them appropriately once they have been used.
Dr Schep said any concerned parents should take their child to the hospital for an x-ray.