That's it from Acting Superintendent Parry.

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"The alleged offender has been speaking freely with police — whether that's cooperation or not, but he hasn't not commented at this stage," Acting Superintendent Parry said.

"We have been in contact with the man's family."

One of the two people injured during the shooting — the person who received emergency surgery — was believed to be in the backseat of a vehicle when he was shot.

"They were a passenger in a vehicle which had a number of other family members in it," Acting Superintendent Parry said.

"My understanding is that the injuries are not life-threatening and he is expected to survive thankfully."

He described the situation as "highly traumatic" for the family in that car who then drove immediately to hospital.

"All the persons in the car were adults. There were three persons in the car."

"In my 35 years in the police there's been very few instances of this nature where somebody is randomly targeting people in the street driving past," Acting Superintendent Parry said.

"The male person [in custody] has no recorded mental health history with us. He's been assessed in relation to physical and mental health injuries ... he's been deemed suitable to return to custody [after being released from hospital]."

At about 9:30pm on Sunday, the alleged gunman was arrested at a unit above a business on Georges River Road where the shots were believed to have came from.

"That was his premises," Acting Superintendent Parry said.

Acting Superintendent Parry confirmed that "up to 50 bullets" were fired.

With the crime scene still being investigated, he said that exact number of confirmed shots fired could increase.

Police locked down 300 metres around the area of the scene given the alleged gunman was "wantonly shooting at cars as they drove past these residences".

Geotargeted messages were distributed to the public amid the active shooting situation, according to police.

Traffic plans and diversions were also enacted, and NSW Fire and Rescue also assisted in traffic control.

Acting Superintendent Parry is now reflecting on the "highly dangerous operation" that occurred on Sunday night and the impact to the community.

"Police put themselves at serious risk of death or injury.

"I have examined a number of the [police] cars involved. One shot was fired through the window ... If the police vehicle was occupied at the time, that police officer in all likelihood would have sustained fatal injuries."

Acting Superintendent Parry said it was "incredible" that nobody died as a result of this shooting.

A 30-calibre rifle was seized from the scene.

"The search is still ongoing," Acting Superintendent Parry said.

As for how the man allegedly ended up with a rifle like this, Acting Superintendent Parry said it would form part of their investigation.

"Once we establish through interviewing him, we'll be able to provide facts in relation to that," he said.

Investigators hope to determine the motive during their interview with the man later this afternoon.

"We will [then] have a better understanding of his motivation for why he has done what he has done," Acting Superintendent Parry said.

He confirmed the alleged gunman does not have any links to gangs, organised crime or terrorism associations.

The alleged gunman "does have a couple of children" and very few prior interactions with police, Acting Superintendent Parry noted.