The 30-year-old mother of a newborn boy left in a western Sydney stormwater drain has been charged with attempted murder.

Police said the wowman, from Quakers Hill, she was found after hospital record checks and doorknocks.

She was refused bail on Sunday afternoon and will appear in Blacktown Local Court today.

Police will allege the baby, believed to have been born on Monday, was placed into the drain on Tuesday.

The child was discovered in a drain next to a bike track that runs along the M7 about 7.30am on Sunday after passers-by heard its cries.

It took seven people to lift the drain's concrete lid.

"That baby wouldn't have lasted an hour and a half," said cyclist David Otte, who was one of those who discovered the newborn. The baby was wrapped in what appeared to be a hospital blanket.

"We couldn't see it but we could hear it. It was distressed."

The boy, now thought to be one week old, is in a serious but stable condition at the Children's Hospital at Westmead.

Police had earlier said there had been "unconfirmed reports" that a man in an orange shirt and of Indian appearance had been seen along the cycleway shortly after the baby was discovered.

It was believed the boy fell 2.5 metres to the bottom of the drain after being pushed through the narrow gap beneath the concrete lid.

Department of Family and Community Services district director, Lisa Charet, said such incidents were rare.

Post-natal depression, or very young mothers who did not know where to turn for help had been factors in previous cases, she said.

"I think you have to be in a fairly desperate place to commit this sort of act and that's where we'd rather people come forward and get the support they need," Ms Charet said.

Inspector David Lagats, who counted among those who helped retrieve the boy, said initially "we all thought the worst".

'It's a horrific incident ... but with all the team work from the bystanders, too, it was a good result and hopefully the child will survive," he said.