Chautauqua County – A 6-year-old girl and 4-year-old boy died at the scene of a car accident late Monday when the vehicle overturned after hitting the embankment.

Police say Katherine Ambrusko, 6, and her brother, Peter, 4, were pronounced dead at the scene, after the car their father was driving drifted off to the side then struck the embankment. Their father, Dr. Steven J. Ambrusko, 35, was taken to Brooks Memorial Hospital for head and back injuries.

“It’s unknown, really, what caused the accident,” State Police Capt. Michael Nigrelli said. “There was no indication of any drug or alcohol involvement.”

A witness driving behind Ambrusko’s car said that they saw his car drift to the right of the road with no apparent reason.

Investigators say that it is possible that the father had fallen asleep while driving. The investigation is still ongoing.

According to reports, both children were in child-restraint and were secured properly.