Police say it was lucky nobody was hurt when a truck smashed into a car in Melbourne's north and pushed the vehicle several kilometres before the driver of the semi-trailer realised what had happened.

A man was driving along the Hume Freeway at Thomastown when the truck clipped his car as it changed lanes around 5:30pm on Wednesday.

His car became wedged on the front of the truck and was pushed along the road for several kilometres.

The man stuck in the car managed to get the truck driver's attention by waving bright orange electrical equipment out of his window.

Senior Constable Scott Cowan says the wet conditions were a factor in the crash.

"We're seeing a lot of rain in the area tonight which is impacting on visibility so we urge everyone to slow down and drive to the conditions," he said.

"It's lucky that no-one was hurt in this incident and it could have had a far worse outcome."

The truck driver will receive infringement notices over the crash.