A large forklift lies on its side after one person was killed and seven others were injured after a multi-vehicle accident. PHOTO: KEVIN WARN, OCR

A driver was killed and seven others injured when a forklift became airborne and crashed into cars on a California freeway.

Investigators are still trying to work out why the driver of a rig carrying the forklift swerved and crashed through the concrete divider, according to the Orange County Register.

The victim was identified as 28-year-old Eric McEntarffer, who was driving on the other side of the road when the forklift and another car came crashing through the centre divider in front of him, wrecking three other cars before the truck driver drove straight into him.

The crash that also injured seven people and wrecked nine cars caused several lanes in each direction of the freeway to close overnight.

The Register reports that Daniel Gregory Delara, a 28-year-old truck driver, was driving a rig carrying a heavy forklift in a slow lane of the freeway when something went wrong.

Officials can't explain the accident in which Delara swerved and hit another vehicle.

The forklift, which weighs thousands of pounds, could not be easily moved because it fell sideways and a wheel was disabled, according to the report.