Cars have been showered in cement during a terrifying few moments that left motorists driving blind on a busy highway.

An avalanche of the building material was let loose on Perth’s Tonkin Hwy on Friday when a truck’s tailgate was suddenly opened after it went over a bump.

WATCH THE VIDEO ABOVE: Dashcam captures car showered in cement on busy Perth highway.

Know the news with the 7NEWS app: Download today

Tyler’s Subaru WRX was completely covered, and his wipers were unable to clear the mess on his windscreen.

Despite being in shock, he managed to safely steer his car to the side of the road near Bayswater.

“I was thinking about swerving ... but I kept my cool,” he told 7NEWS.

‘It was a really out of body experience. I didn’t understand what had happened until after when it really kicked in.

“I didn’t think it was as bad until I actually saw what the remains were on the car.”

By then the truck was gone.

Tyler, 26, has given his car a wash but the windscreen was chipped and the paint has been damaged.

His dashcam captured the truck’s numberplate and a report has been filed with police.

“I do have my hopes up that the damages will get fixed,” he said.

The right lane of southbound traffic just before Great Eastern Hwy was closed for more than two hours so Main Roads could clean the mess.