French authorities are investigating whether a passenger train derailment in Normandy on Friday evening was a deliberate act of sabotage.

The train was travelling between Rouen and Caen when it derailed near Cléon, just south of Rouen, shortly before 20:00 local time (18:00 GMT). According to reports, 186 passengers were on board.

Forty-four people were treated for injuries. An 18-year-old woman was airlifted to hospital in a critical condition, though prosecutors later confirmed her life is no longer in danger.

"At this stage, the leading theory is that a piece of rail was present on one of the tracks, potentially causing the derailment. The reason for its presence is unknown," prosecutor Sébastien Gallois said on Saturday.

Gallois added in a press release: "The train's 'black box' has been seized. Several interviews are scheduled, and a court-appointed expert has been called in."

He also provided an update on the injured: "The main victim is still in hospital but her life is no longer in danger. The other victims have received care and treatment; they have either been discharged or are about to be."

The Rouen prosecutor's office confirmed the train driver had tested negative for drugs and alcohol.

Some 140 firefighters and other emergency teams were deployed to the crash scene immediately after the derailment.

A passenger named Louis described the moment of impact to a local radio station. "Suddenly there were a few jolts, and then after about three seconds it got stronger and stronger," he said.

"I couldn't stay in my seat anymore. The windows partially shattered, the stones from the track came into the carriage. It was really shocking. I'm still shaking," he added.