The girlfriend of actor Keanu Reeves was killed when her car overturned in an early-morning crash in Los Angeles, police confirmed last night.

Jennifer Syme, 29, died instantly when her Jeep Cherokee four-wheel drive hit three parked cars and overturned in Hollywood, partly throwing her out of the vehicle.

Ms Syme had been treated for depression after her baby daughter was stillborn in January last year but Los Angeles police last night said it was not known if drugs or alcohol had been a factor in the crash.

The crash occurred on Sunday at 6.20am local time (2.20pm BST) when Ms Syme, a record industry executive, was driving along Cahuenga Boulevard in Hollywood.

"The collision occurred after a 1999 Jeep Cherokee, travelling northbound Cahuenga Boulevard, for unknown reasons, collided into three parked vehicles, which were parked on the east side of the street," said a spokesman for the Los Angeles Police Department.

"The collision resulted in the Jeep Cherokee overturning on the roadway, causing the driver to be partially ejected.

"The driver, a 29-year-old female, was instantly killed. "It is currently unknown if alcohol or drugs were a factor in the collision."

Ms Syme and Reeves, 35, had preserved their privacy and never made their relationship public or commented on the loss of their baby.

Reeves' last big hit was The Matrix, where he starred alongside Carrie-Anne Moss, and his other films have included Speed and Dracula.

Later Los Angeles County Coroners department said they were investigating if drugs had played any part in the crash.

Lieutenant Fred Corral said Ms Syme's mother had told the department her daughter was being treated for both back pain and depression following her daughter's death.

"We found some medication which we believe to be prescription drugs the deceased was receiving," said Lt Corral.

"Two one dollar bills which were rolled-up with a white powdery substance were also found inside the vehicle."

Lt Corral said an autopsy had been carried out on Ms Syme's body today but further toxicology tests were to be carried out to determine the cause of death.

Ms Syme had suffered massive head injuries and police declared her dead as soon as they arrived at the scene.

"Ms Syme's mother indicated that she had no history of narcotics use," said Lt Corral.

"She was under the care of a doctor for back pain. She was also being treated by another doctor for depression following the death of her baby daughter last year."

Lt Corral said it was unclear when the cause of death would be finally determined.