Part of excavator bucket hits car on Australian motorway

An Australian motorist has suffered serious head injuries after the bucket of an excavator fell off the back of a truck and hit her sports car, causing it to flip.

Emergency services were called to the eastbound lanes of the M5 at Hammondville, Sydney, following reports an Alpha Romeo was involved in a crash at 7am (10am NZ time) on Wednesday.

The woman, in her 20s, was treated for serious head injuries and a possible arm fracture and was taken to Liverpool Hospital in a stable condition, police say.

They were speaking to the driver carrying the excavator and appealing for witnesses.

Eastbound lanes reopened an hour and a half after the incident and motorists can expect delays with traffic queued back 13 kilometres.

 - AAP