A baby girl in Toronto was born in sub-zero temperatures, rushed to hospital, pronounced dead and placed under a sheet before two police officers noticed she was still alive on Sunday morning.

The story started in a part of northwest Toronto where a 20-year-old woman reportedly gave birth outside on a day when the temperature went as low as -16 C during the morning hours.

In a telephone interview, Toronto police Const. Wendy Drummond said the child's mother "wasn't feeling well" on Sunday morning and decided to go to the hospital.

"She and her mother were walking to the hospital and it was en route that she in fact gave birth," Drummond said.

The child's mother, the newborn and the grandmother were taken to Humber River Hospital's Finch Avenue campus via ambulance.

Staff Sgt. Norm Proctor said the child was "worked on" in the trauma unit of the hospital with vital signs absent, but pronounced dead "after some time" and subsequently put under a sheet.

Two officers were then guarding the infant, while the coroner travelled to the scene.

"As per police protocol, officers remained with the child awaiting the arrival of the coroner, so that the death could be further investigated and the circumstances," Proctor said in a telephone interview with CBC News.

Some two hours after the initial call, the officers saw the sheet move. The baby, it turned out, was alive.

"In this particular situation, it was a matter of being in the right place at the right time," Drummond said.

"The officers were on a very sad detail…it was when they noticed the sheet moving that they were able to investigate a little bit further and detect a pulse."

The newborn is now in stable condition, police said. Drummond said the mother remains in hospital, but is in good condition.

Proctor said it was an unusual story with a happy ending.

"We work in an area where there's a lot of hard luck and negative stories that take place so this was a good story and at 31 Division, we’re all very happy about it," he said.

The officers involved in the situation did not want to speak to media about what had happened, Proctor said.