A 19-year-old man has been arrested after a tragic car crash that killed a woman and the unborn child of another.

Just before 3am on Sunday, Newcastle police officers saw a Holden Commodore allegedly being driven dangerously, but did not pursue it due to safety concerns.

A short time later, after allegedly again crossing to the wrong side of the road, the Commodore was involved in a head-on collision with another car.

A passenger in that car and believed to be aged 55 was found dead. The 28-year-old driver, who was pregnant, suffered serious leg injuries and remains in a serious condition in John Hunter Hospital.

Police later confirmed her unborn child had died.

The two women are believed to be mother and daughter.

The driver and front passenger of the Holden allegedly fled before police arrived. The two rear passengers – two girls aged 15 and 17 – remain in serious conditions.

NSW Police said a 19-year-old man was arrested at a home in the Newcastle suburb of Mayfield shortly after 3pm on Tuesday.

“He was taken to Waratah Police Station where he is assisting police,” they said.

Police have also spoken with a 17-year-old girl believed to be the front passenger of the vehicle.

“This is a horrible incident [and] what’s occurred is truly tragic,” acting assistant commissioner Paul Dunn said.

“Two women driving around innocently, one has lost their life, one has lost their unborn child.”