Thieves smashed their way into more than 20 cars in Hamilton overnight in a spate of thefts which may have been committed by the same offenders.

Reports of a four-door silver sedan speeding off from a theft on East St about 3am today prompted a police investigation.

"In all we've found 20 cars broken into, mostly in an area around Claudelands between East St and Pearsons Ave but also a few cars as far away as Dinsdale," acting Sergeant Murray MacDonald said.

"All had been parked out on the road and had either their quarter window and driver's side windows smashed with a variety of items taken.

"So far we only know of cars parked out on the street being affected."