Five people were arrested after the remains of a baby were found at a house in Marsh Green, Wigan, according to media reports.
Greater Manchester Police (GMP) said they were arrested on suspicion of concealing a death and unlawful burial.
They are aged between 20 and 70 and later released on bail pending further enquiries.
The police have sealed off the Wigan property and another scene in Valley Road, Pemberton.
Chief Superintendent Clare Jenkins from GMP's Wigan described the discovery as "heartbreaking".
She assured that several teams of officers and specialist resources are at work and they will find out more about the circumstances surrounding this incident.
"We are confident that this is isolated and there is no threat to the wider public," she added.
