The crash occurred at a level crossing on Henry's Lane at Coralville, about 30 kilometres north-east of Taree, just after 11am on Thursday.

Police said those in the car at the time were a woman, aged 30, and three girls, aged two, six and seven. The victims are believed to be a mother and her daughters.

The northbound train appeared to have taken several hundred metres to stop after the collision, while the station wagon came to rest on its side next to the crossing.

Emergency services personnel from the Volunteer Rescue Association worked for more than an hour to free the trapped occupants.

Two Westpac Rescue Helicopters and a NSW Ambulance helicopter landed in a paddock about 100 metres from the crash site.

The two-year-old girl, who suffered critical head injuries, was placed in an induced coma before she was taken by helicopter to Newcastle's John Hunter Hospital. The helicopter left the accident site at 1.15pm and arrived in Newcastle at 2pm.

A second helicopter carried the seven-year-old girl, who sustained serious head injuries.

NSW Ambulance paramedics treated the six-year-old girl for shock and minor injuries, while the woman was treated at the scene for serious injuries.

The third helicopter reportedly transported the woman and the six-year-old to John Hunter Hospital.

It is believed the family live in the Manning Valley.

Line of emergency services on scene at site of accident Coralville- reports suggest four occupants in car @nbnnews pic.twitter.com/Fo54jpUxmt— Sally Rafferty (@sally_rafferty) April 21, 2016

A Westpac Rescue Helicopter spokesman said the woman was pregnant.

The train driver was treated for shock and was taken to Manning Hospital in Taree for mandatory blood and urine testing.

Officers attached to Manning Great Lakes Local Area Command, with help from the Crash Investigation Unit, have set up a crime scene at the level crossing and are investigating the cause of the crash.

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With Manning River Times