A 31-year-old man has been arrested on suspicion of attempted murder after a newborn baby was found in hospital toilets.
The abandoned infant had to be resuscitated after being discovered by security staff just after midnight at Wigan's Royal Albert Edward Infirmary.
The A&E department, where the discovery was made just after midnight, was closed for a time but has now reopened.
"This is an awful situation, I am just so happy I am able to say that the baby boy is doing well," said Detective Inspector Martin Reddington.
"We are appealing for anyone who may have been in the A&E department between 7pm and midnight and perhaps saw a man and a woman in and around the toilets or saw anything unusual to get in touch with police as soon as possible.
"I would like to take this opportunity to praise the staff at the Royal Albert Infirmary.
"Without doubt their heroic actions saved the life of this newborn baby."
The chief executive of Wrightington, Wigan and Leigh NHS Foundation Trust, Andrew Foster said: "I would like to thank all staff who were involved for their professionalism and calmness during the incident, particularly the diligent member of staff who discovered the baby and raised the alarm.
"I'm very proud of the way our staff worked.
"Their quick response without doubt saved the baby's life."
Anyone with information is asked to call police on 0161 856 7124, or Crimestoppers, anonymously, on 0800 555 111.