The Waitaki Transport premises was ransacked at the weekend.
Between 9am on Saturday and 9am on Sunday, windows were smashed and a building entered.
"At this stage, nothing has been stolen, but someone has gone in and all the drawers have been tipped out,'' Sergeant Tony Woodbridge said.
"It's a bit of a mess in there.''
Investigations were continuing.
Police urged anyone who might have seen anything suspicious in the Waitaki Transport area, in Oamaru's north end, on Saturday or Sunday to contact the Oamaru station on (03) 433-1400.
Alternatively, information can be provided anonymously via Crimestoppers on 0800 555-111.
