Two teenagers are reportedly dead and their mother is injured after a shooting in Sydney's north east.

With AAP.

A teenaged girl and boy have been shot dead in a suspected domestic violence-related attack at a home in Sydney’s northwest.

Police were called to reports of a fatal shooting at a West Pennant Hills home about 5.20pm on Thursday, a NSW Ambulance spokesman told AAP.

They say the teens were found dead at the scene.

Paramedics were also treating a third victim, he said, a woman in her 30s who is widely thought to be the victims’ mother. It’s believed she is being treated for shock in an ambulance outside the home.

The teens were found dead in a bedroom, NSW Ambulance Inspector Kevin Sweeney told reporters at the scene on Thursday evening.

“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.

“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, Det Supt McFadden said.

Ryde detectives are being assisted by detectives from the State Crime Command’s Homicide Squad.

John Howard who lives just 50 metres along Hull Road from the house, says he’s 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.”

More to come.

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