A convenience store clerk had to lock himself in a back office when a thief smashed his way into the store overnight.

Investigators said the crook smashed through the front door of the Timewise store on Lathrop Street and the East Freeway just after 2 a.m. Thursday.

Police said the male clerk saw what was going on, ran to the back office and then locked himself inside.

Detectives said the suspect grabbed the entire cash register and ran off with it. Police said he got away with about $100.

Police said video cameras inside the store could help them track down the suspect, but so far, they have not released a suspect description.