A newborn baby girl is in hospital after being found wrapped in a towel in a shopping bag on a London street, British police said on Friday as the capital was experiencing sub-zero temperatures.

The baby was found by a person walking their dog in Newham, east London, just after 2100 GMT on Tuesday, London's Metropolitan Police said. According to the national weather service, it was minus 3 degrees Celsius in London at that time.

"That person kept the baby girl warm until London Ambulance Service paramedics arrived and checked her over before taking her to hospital," Chief Superintendent Simon Crick, who leads policing in Newham, said in a statement.

"I am delighted to report that she wasn’t injured in any way and is safe and well in the care of hospital staff."

Police said they were concerned for the welfare of the baby's mother and appealed for her to get in touch.