A 25-year-old man has been arrested after two children were killed and three others injured when they were struck by a car in rural New South Wales yesterday.

Four boys — aged six, seven, nine and 10 — and a 34-year-old woman are believed to have just been at the local pool when they were struck on Warne Street in Wellington, near Dubbo and about 350km north-west of Sydney, about 4.30pm.

Ambulance paramedics treated the group at the scene, however the two youngest boys died a short time later.

The woman was airlifted to Westmead Hospital in a critical condition.

The 10-year-old boy sustained serious leg injuries and was airlifted to The Children's Hospital at Westmead and is undergoing surgery.

The nine-year-old boy sustained minor injuries and was taken to Orange Base Hospital.

NSW Police said the driver of the vehicle left the scene before officers arrived.

Acting Superintendent Natalie Antaw said police located the 25-year-old Wellington man just after 8.40pm and arrested him "after a short foot pursuit".

"He has been taken to Dubbo Police Station to assist police with inquiries."

NSW Ambulance Superintendent Andrew DeGabriel said paramedics were confronted by a tragic scene.

"These types of incidents are shocking for all emergency services and witnesses involved," he said.

"We were confronted with an absolutely devastating scene in Wellington.

"It's heartbreaking for this to happen to such a small community."

Thirteen ambulance crews and four specialist medical teams via helicopter were dispatched to the scene, Mr DeGabriel said.

Forensic police and crash investigation unit officers will examine the crime scene, which is being guarded by police overnight.

"Obviously it's tragic circumstances for the entire community and our thoughts are completely with the family and friends of the little ones involved and also the rest of the community of Wellington," Ms Antaw said.

"Obviously a scene like that is horrific for anybody."

Ms Antaw said the investigation was ongoing and urged anyone with information or CCTV or dashcam footage to contact Crime Stoppers on 1800 333 000.