The two dogs that mauled a 40-year-old man at a house he was visiting in Sydney's west have been put down

The American Staffordshire terriers were euthanised this afternoon, a Blacktown City Council spokesperson confirmed to AAP.

The man is in a critical condition in Westmead Hospital after suffering serious injuries to his ears, face, abdomen and chest in the dog attack about 1pm yesterday.

The dogs - a male and a female - are described on their registration as American Staffordshire terriers. (Nine)

He went into cardiac arrest and had to be resuscitated and given a blood transfusion.

A girl aged between seven and 10 was also bitten on the back, while her mother was bitten on the forearm, NSW Ambulance Inspector Phil Templeman said.

"Ambulance paramedics were on the scene in minutes and found quite a distressing scene," he said.

A number of people in the street had blood on them after trying to help control the dogs at the "horrific" scene, he said.

The dogs were sedated by RSPCA officials before they were taken away. (9News)

Police, paramedics and RSPCA officers were on the scene. (Nine)

The dogs had been taken into another room and locked in there by the time emergency responders arrived.

Animal welfare group RSPCA NSW was called in by police to tranquillise the medium-sized dogs at the property.

They were taken to a local veterinary clinic and spent Thursday night in the council's animal holding facility.

Three people including a child were bitten by dogs in Sydney's west. (Nine)

Officers from Mount Druitt Police Area Command are conducting investigations.