Police in Australia have questioned but not charged a woman whose newborn baby was found abandoned in a drain near a Sydney motorway.

The baby boy, who is only a few days old, is in a serious but stable condition in Sydney's Westmead Children's Hospital, police said in a statement.

The 30-year-old mother was taken to Blacktown Hospital in Sydney after being questioned by detectives, police said. No details on her medical condition were released.

A group of cyclists were riding on a cycle lane beside the M7 motorway in the Sydney suburb of Quakers Hill when they heard a baby's cry coming from the drain, police said.

They managed to lift the heavy concrete lid off the drain, which is 8ft deep, and saw the baby wrapped in a hospital blanket at the bottom. Police reached the scene soon after and rescued the child.