A 24-year-old man from North Yarmouth was seriously injured Friday evening in a crash in Pownal, Maine State Police said.

Robert Morrison was headed south on Route 9 around 7 p.m. when his 2010 Chevy Impala went off the road and hit a tree, said Trooper Joe Bureau. No other vehicles were involved and there were no passengers in Morrison’s car, he said.

Morrison suffered head injuries and was taken by helicopter to Maine Medical Center in Portland, Bureau said. A nursing supervisor at the hospital said she had no information on Morrison’s condition late Friday night.

Bureau said police are still investigating the crash, which occurred on a straight portion of the road, and don’t yet know the cause. He said speed had been ruled out as a factor.