A man has been caught driving 120km/h over the speed limit in Melbourne's outer west.

Police said the 21-year-old was clocked at 200km/h in an 80km/h zone on Middle Road, Rockbank, at 12.30pm Wednesday.

A Victoria Police spokeswoman said the driver's car, a 2015 Volkswagen Golf, was impounded at a cost of $983.

He will be charged on summons with speeding and other traffic offences, the spokeswoman said.