A teenage girl and boy have been shot dead at a home in Sydney's north-west in what police have described as an "horrific" suspected domestic violence-related incident.
They say a person of interest has been identified and a search for the gunman is underway.
Officers were called to a home in Hull Road at West Pennant Hills about 5.20pm on Thursday after reports of shots fired.
The teens were found dead in a bedroom, NSW Ambulance Inspector Kevin Sweeney told reporters at the scene on Thursday evening.
AAP
"When ambulance paramedics arrived ... we were confronted with an extremely distressing and stressful situation," he said.
"Two teenagers were unfortunately deceased in their bedroom and unfortunately at that time there was nothing we could do to help them."
Their mother arrived shortly after police and was treated by paramedics for severe shock.
Police Acting Region Commander Brett McFadden told reporters the attack was believed to be domestic violence-related with a person of interest on the run.
It was unknown how many shots had been fired, Detective Superintendent McFadden said.
Emergency services had arrived to an "horrific scene", he added.
AAP
"It was a very harrowing experience for emergency services who responded.
"You've got a family that is going to struggle to come to terms with it and emergency responders will struggle to come to terms with what they have seen."
Police were speaking with neighbours while an extensive forensic investigation was underway, Mr McFadden said.
Ryde detectives are being assisted by detectives from the State Crime Command's Homicide Squad.
A local resident John Howard, who lives just 50 metres along Hull Road from the house, said he was shaken.
"I could hear the police helicopter and then I saw it all over the television," he told AAP.
"It's a friendly, quiet street."
