Detective Sergeant Mark James, of the Hamilton police crime investigation unit, said that an offender approached a jewellers about ​7.30pm on Saturday in Hamilton's Gray Street and punched a hole in a window.

He then reached in and stole a handful of rings before running off.

"The restaurant across the road was full at the time and there were two women coming out of Subway after getting dinner only a couple of metres from where the smash-and-grab took place at the time," he said.

"The offender has cut himself in the process of committing the crime and there is security camera footage that's being examined by police members.

"Items from the store were discarded nearby and forensic examinations are being conducted in relation to the crime scene and the discarded items."

​Detective Sergeant James​ said the offender was wearing bone-coloured shorts and a white T-shirt over the top of a black jacket.

"He's raced off with a handful of rings but the potential loss to the business could have been far greater," he said.

​"The offender would best be described as disorganised and desperate. Anyone with information about the crime is requested to contact Crime Stoppers on 1800 333 000 or the Hamilton police station.

"We're looking for someone who was wearing shorts on Saturday night who has suffered a cut to his hand or arm.”