The mother of two children shot dead at their Sydney home by their father has released photos of her son and daughter, as friends, family and the community come to terms with the shocking murders.

Jack Edwards, 15, and Jennifer Edwards, 13, were killed just before 5.20pm on Thursday at their West Pennant Hills home in what police say was a "planned attack" by John Edwards, a 68-year-old financial services worker.

Police say the teens were at home alone and attempted to hide in a bedroom as their father barged in the house carrying the handguns.

After an overnight search, police discovered Edwards' body at his home in Normanhurst, a suburb on Sydney's Upper North Shore, about 5 kilometres from where the children were killed.

Two guns, described as "powerful handguns" by police, were also found at the property.

The children's 36-year-old mother Olga returned to her home shortly after police arrived.

Floral tributes outside home

Outside the home in West Pennant Hills on Saturday a steady stream of mourners came by to pay tribute to the two teenagers.

Flowers outside the West Pennett Hills home of Jack and Jennifer on Saturday. ( ABC News )

Most laid flowers outside the home, while some mourners became emotional as they stopped to pay tribute.

A GoFundMe page has been set up by a Russian group in Australia to raise money for Ms Edwards' mother to fly out to Sydney.

'Port Arthur moment' for gun reform

Police said Edwards had been involved in custody hearings over the two children during the past two years.

Since the shooting, questions have been also been raised over Edwards' ability access to firearms, after it emerged he was rejected from gun clubs and police confirmed he had a violent history.

Emeritus professor of public health at Sydney University Simon Chapman said Thursday's tragedy should force authorities to talk about gun reform to stop domestic violence incidents.

"The incident that we've just seen, and the one in Margaret River, Davidson and Wagga a few years ago, all domestic killings, these should be the Port Arthur moments for gun reform in this respect," he said.

He said in Canada, for example, ex-spouses are interviewed by licencing authorities on whether they should have access to guns.

John Edwards, 68, has been identified by police. ( ABC News/LinkedIn )

Both sides of NSW politics said they would consider the reforms in light of Thursday's shooting.

It is understood Edwards registered for his firearms licence in late 2017.

It has been reported he purchased several guns — including the ones he would ultimately use on Thursday night — as a registered gun licensee.

'Stress and heartache'

NSW Police Acting Assistant Commissioner Brett McFadden said the children's mother was in shock after attending the scene two days ago.

"I can't even imagine the stress and the heartache that she is going through right now," he said.

"It is a horrific homicide … this is a most traumatic incident."

Sorry, this video has expired Police were called to a house on Hull Road in West Pennant Hills about 5.20pm

While Edwards was known to police, Commissioner McFadden said he had no "contemporary" criminal record.

"The … nature of the relationship, particularly in recent times and the level of access that the 68-year-old had to his children is subject to investigation," Commissioner McFadden said.

Following the incident on Thursday night, NSW Ambulance Inspector Kevin McSweeney said when paramedics arrived at the scene they were confronted with "an extremely distressing and stressful situation".

He said there was nothing that could be done for the boy and girl.

A tribute card to Jack and Jennifer laid out the front of the West Pennant Hills home on Saturday ( ABC News: Ross McLoughlin )

The family and emergency services personnel who attended the scene are being provided with support.

"You've really got a family that's going to be struggling to come to terms with it but also the responding police will struggle to come to terms with what they've seen."

Neighbours shocked

Directly after the shooting on Thursday, neighbour Maya Clarke said she was shocked and scared to hear of the tragedy.

"It's just a nice place, a nice area," she said.

"How people can shoot kids … I'm shaking."

Her granddaughter Sienna Clarke said it was a quiet and peaceful area.

"Bad things don't happen around here so it's just kind of frightening because our house is just down the street," she said.

ABC, wires