A newborn baby boy has been found alive down a drain near a major motorway at Quakers Hill in Sydney's west.

Cyclists riding the track alongside the M7 heard the baby crying about 7:30am this morning.

They had to lift the top off the drain, which was about 2.5 metres deep, to reach the child.

Inspector David Lagats said officers were horrified by the discovery.

It appears the baby was dropped about 2.5 metres into the drain.

Despite having no physical injuries, Inspector Lagats said it is unlikely the baby would have survived today's heat if he was not found.

"It was already undernourished and dehydration would have taken effect," Inspector Lagats said.

Police think the baby was born in a hospital but dumped in the drain soon after. It had most likely been there for several hours before it was found.

"It would appear from the striped blanket, it is similar to what babies have in hospitals," he said.

"The umbilical cord had been clamped and cut. It seems to have had medical intervention.

"We are looking at local hospitals as to babies born in the last couple of days which may match that description."

New South Wales Police are urgently trying to find the baby's parents and released a photo of the baby on Twitter.

A cyclist reported to police seeing an Indian man wearing an orange shirt walking in the area at the time.

Inspector Lagats said he is confident of finding the child's parents by the end of the day.

The baby has been taken to Westmead children's hospital for precautionary checks.

'We want mum to come forward'

The baby boy is most likely to be placed in foster care until his parents are found.

Family and Community Services district director for Western Sydney Lisa Charet said the parents must be feeling desperate.

"Often when this sort of thing happens, people are in a place of desperation," she said.

"There has been cases where mothers have had postnatal depression or those issues or are very young and don't know where to go to for help. That's where we come in because we can provide help.

"We are really worried about primarily his welfare and mum's. We would want mum to come forward.

"We can give her the help and support she needs. She must be feeling distressed.

"If the parents come forward, we will be able to work with them to find out what support, what they help need and be able to assess where we go from here. It depends on the circumstances going forward."