A 70-year-old grandfather has suffered serious injuries in a brutal dog attack in Sydney's southwest.

Charlie Mifsud was walking home from shops in Campbelltown on Wednesday afternoon when he was attacked by his neighbour's Staffie-cross, named Leila.

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Security video, given to 7NEWS, shows the dog - which was wearing a white Elizabethan collar - lunging at Mifsud.

The collar is a protective device placed around a pet's neck, typically after surgery, to prevent the animal accessing any wounds as they heal.

'Get off me'

Mifsud's wife, who was watching TV inside their home, says she ran outside after hearing what she first thought was a dog fight.

"I heard the yelling and the screaming, and 'Get off me, get off me' so I ran out the front," Denise Mifsud told 7NEWS.

"Charlie by that time is laying on the road, the dog's on him, and I think 'Oh my God'."

Security video shows the dog - which was wearing a white Elizabethan collar - lunging at Misfud. Credit: 7NEWS

The attack came to an end only when the dog was pulled away by its owner.

Denise says her husband was very shaken and in agony after the dog jumped at his arm and "ripped it to pieces".

"He was screaming with the pain of his arm," she said.

"It jumped up at him and grabbed him by the arm.

"The jumper is not even ripped but the bite was so fierce it's cut right through, it could be to the muscle in the arm."

Chevron Right Icon 'He was screaming with the pain of his arm.'

The grandfather-of-five was taken to Campbelltown hospital and may need surgery to treat the wounds.

His family believes he would have lost his arm or even his life had the attack gone on for any longer.

Despite the ordeal, they don't want to see Leila destroyed, rather they want the dog removed from its neighbour's home.

"I want it taken away, I think once it's done that you can't trust it."