Officers were called at about 13.15 BST on Sunday by the north-west ambulance service after reports a child had been injured at Carr Lane in the town of Milnrow.
The toddler was taken by ambulance to hospital where he was pronounced dead.
No arrests have been made and police are investigating the circumstances, as well as previous incidents involving dogs at the home.
Detective Superintendent Jamie Daniels, of the force’s public protection and serious crime division, said: “This is a tragic, devastating incident and our thoughts are with the family at this horrendous time.
“We are investigating the incident and previous incidents involving dogs at this address.
“While our inquiries to find out what happened will be thorough and are very much in their infancy, we suspect that this little boy has, sadly succumbed, to injuries received as a result of a dog attack.
“I understand this is an extremely distressing incident for all concerned and this news will rock the local community.
“I can only assure everyone that we will work relentlessly to establish the full circumstances that led to this tragedy and while we retain an open mind, this is now being dealt with as a criminal investigation.
“There will be a significant police presence in the area, we will be there to carry out an investigation and address any concerns residents may have.”
Police are calling on anyone with information to call 0161 856 5413 quoting incident 1615.