A mother, father and their baby daughter died, and two other children were injured when a car carrying the family of five careered off the road into a tree near the Victoria-South Australian border.

The crash happened at 7:30am near Lake Mundi, outside Casterton, about 400 kilometres west of Melbourne.

The father, who was driving the car, was freed from the wreckage by the CFA after being trapped for more than two hours.

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He was taken to the Mount Gambier Hospital in a critical condition and died on Sunday afternoon.

A boy also suffered critical injuries and a girl suffered minor injuries.

Both were flown to the Royal Melbourne Hospital.

It is believed the family were on a long drive back to South Australia.

Ambulance Victoria spokesman John Mullen said the accident happened on a gentle bend in the road, in a relatively remote area.

“All services, all emergency services were there including the SES, ambulance, police and the CFA,” he said.

Superintendent Don Downs said it was a “tragic collision” and that fatigue was a “big killer” on the roads in south-western Victoria.

“We’ve got the major collision investigation unit coming down to do the formal investigation,” he said.

“It’s a long road. It’s quite a straight road.

“People think they can drive in these back roads and there’s not a big risk but there is a big risk.”

Superintendent Downs said it had been a “horror start” to the year with six people killed on the roads in the area since January.

“When you come out to jobs like this it’s heart-wrenching. Heart-wrenching on the community and heart-wrenching on the members who attended,” he said.

“We’re trying to work out where they started their journey. But it is a long road. We’re only seven kilometres from the South Australian border.”