A distraught dog owner whose family pets mauled and killed an elderly woman says he can't comprehend why the usually 'gentle' animals viciously attacked.

The horrifying incident unfolded at about 7am on Sunday at Collingwood Beach in the Shoalhaven region of New South Wales.

Sally Holland, 91, and her daughter were set upon by the three Bullmastiff crosses, which then attacked three witnesses who stepped in to help.

It's believed the animals escaped their Vincentia backyard by 'busting out the bottom of the fence'.

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One of the Bullmastiff crosses that attacked and killed an elderly woman at a Jervis Bay beach is pictured with young children

Dog-owner Adam Newbold (pictured) breaks down in emotional interview after family dogs attack and kill 91-year-old woman at Jervis Bay

'I never thought in my wildest dreams that this would happen,' dog owner Adam Newbold told Channel 9 in an emotional interview.

'I had my two daughters, we were just playing with them in the yard yesterday afternoon… the kids hang off them.

'I don't understand what is going on. I'm in shock. I don't know what could send them wild.'

Mr Newbold said there was nothing out of the ordinary that could have set them off.

'Fair enough if it was another dog or something but it wasn't even another dog, my missus said.

'They even bit her when she was trying to help the people.'

Devastated by the brutal attack, a tearful Mr Newbold apologised to the victims.

Sally Holland (pictured) was set upon by dogs at a Jervis Bay beach while going for a swim. The 91-year-old died at the scene

Adam Newbold is pictured by a tree speaking with detectives after his dogs escaped his backyard and killed an elderly woman.

'All I can say is that I'm sorry to the people that have been hurt,' he said.

'I've had them for seven years… I would never have had these dogs near my kids if I knew this could happen.'

According to News South Wales Police all three dogs will now be put down and have been seized by Shoalhaven Council rangers.

The other victims of the attack are reportedly in stable conditions.