Man, 74, arrested following shooting on Sydney's north shore

A 74-year-old man was also treated at the scene, for facial injuries. He was arrested before being taken to the same hospital under police guard.

Both men are in a stable condition.

The men are known to each other although it is not believed that both live at the property.

How they are known to each other is still under investigation, Ku-ring-gai Police Area Commander Superintendent Barry Vincent said.

He said two guns had been located in the "front part of the property". The firearms were seized and police will investigate whether they were registered.

Superintendent Vincent added no one else was in the house during the incident.

Just after 2pm, a Fire and Rescue NSW crew arrived to assist police open two doors.

Neighbour Ben Suleymen, 18, was in the garden with his dog when he heard a loud bang followed by inaudible shouting.

"I just heard a massive bang. I didn’t think much of it," he said. "It turned out to be a gunshot."

Mr Suleymen said he had met the elderly man before and he had been "pleasant".

"It's very surprising for around here," he said of the incident. "You wouldn’t expect it."

Seven ambulance crews and a specialist medical team were sent to the scene.

NSW Ambulance Duty Operations manager chief superintendent Tim Fairservice said crews had to make sure the scene was secure and safe before they treated the patients.

"We never really know the extent of the injuries until we arrive on scene," he said.

A crime scene has been established and police remain on scene. Highlands Avenue is closed and members of the public are urged to avoid the area.