Up to 60 cars were vandalised in what has been described as an "unprecedented" damage spree.
Police were called to reports of vehicles with windows, wing mirrors and lights smashed in Colchester at about 07:45 BST on Sunday.
The cars were parked at the Hythe and Whitehall industrial areas on the outskirts of the town.
Car dealer Ray Neal said 20 of his cars were damaged in the attack. He described it as "totally mindless".
Mr Neal, who owns East Anglian Services, said: "I've lived here for 25 years nearly now and we've had minor things but this is totally unprecedented.
"There's no rhyme or reason to it. I'm lost for words and I'm never normally lost for words."
Cars parked on Conder Way, Whitehall Road, Commerce Way and Davey Close were affected, Essex Police said.
The force said the damage happened overnight on Saturday.