The father who shot dead his two children in their north-west Sydney home “premeditated and planned” the execution-style killings during a long-running custody battle with his estranged wife.

John Edwards shot dead his 15-year-old son Jack and daughter Jennifer, 13, in their bedrooms at the home they shared with mum Olga in West Pennant Hills late yesterday afternoon.

He then drove to an address in Normanhurst, five kilometres away, where he turned the gun on himself.

John Edwards was found dead inside a home at Normanhurst after killing his two children yesterday. Olga Edwards has lost her children and her estranged partner in the tragic shooting. Picture: Supplied (Supplied)

A forensic officer stands outside the home where the teenagers were killed. Picture: AAP (AAP)

Edwards had been separated from his wife Olga for a number of years and the pair had spent the last two engaged in a custody dispute over their children.

The 68-year-old was known to police but did not have an extensive criminal history.

A financial planner and volunteer firefighter, John Edwards has been described as a "recluse" by a neighbour.

His brutality against his own offspring have shocked many in the quiet residential neighbourhood.

Residents of Hull Street have returned to their homes after police closed it down after the shooting last night. Picture: AAP (AAP)

The quiet street was turned into a crime scene with police scouring every inch of the West Pennant Hills property. Picture: AAP (AAP)

Staff and students of Pennant Hills High School were informed of the boy's death this morning. Picture: Google Maps (Supplied)

“It doesn’t really sit with what I knew of him,” one neighbour, Ed Corbett, told 9NEWS.

The 68-year-old, who did not live with his children and their mother, also listed himself as a Lions Club member and a volunteer with the Pennant Hills junior AFL club on his LinkedIn profile.

Resident Ryan Attard described a neighbourhood in shock.

“Realising it was right down the street – realising it was right next to me – was pretty shocking,” he said.

Parents get their children ready for school as police continue to scour the area. Picture: AAP (AAP)

Ms Edwards arrived at the home she shared with her teenage children shortly after police made the horrific discovery yesterday evening.

She was treated by paramedics for severe shock and is understood to be in the care of family.

“As a mother, I can’t even imagine what the mother must be going through,” another neighbour Sharon Hillbrick said.

Police and ambulance first responders have also been receiving support following the shocking discovery.

Police are continuing to scour the property where two teenagers were found shot dead in West Pennant Hills. Picture: 9NEWS (Nine)

Police have removed the bodies of the victims from the home. Picture: 9NEWS (Nine)

“Nothing can prepare you to walk into a home and see two children in that state,” Acting Assistant Commissioner Brett McFadden said today.

“This is something that has been premeditated and planned.”

He had earlier described the murder scene as “harrowing” and “what can only be described as horrific”.

The siblings were found dead from gunshot wounds in their bedrooms, sparking an intensive police search for their father, whose body was found at the Normanhurst property early this morning.

Two handguns registered in the shooter's name were found at the Normanhurst property, but police say these were not the only weapons the 68-year-old owned.

Students at Pennant Hills High School, where the older boy was a student, were informed of their classmate's death at an assembly this morning.

(Nine)

The principal held a meeting with his staff before students arrived, and every child was given a letter to take home to their parents.

Counselling and support services have been offered to students and staff at both Pennant Hills High School and Jennifer's school, Gosford High School.

Residents of Hull Road were allowed back into their homes today after police shut the street down to investigate the teenagers' deaths.

"We understand that those handguns came into his possession lawfully earlier this year," he said.

Ryde police and the State Crime Command's Homicide Squad are investigating. Picture: AAP (AAP)

When police arrived at the West Pennant Hills home, they found the bodies of the two teenagers. Picture: AAP (AAP)

The bodies of the teenage victims were removed from the West Pennant Hills home in the early hours of this morning.

Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.