Fire and Emergency New Zealand said it was notified of the blaze at 7.57pm on Tuesday.
The restaurant is in Thames St and is located right next to the Oamaru Cinema.
Four fire trucks in total were dispatched and a police cordon was in place.
They were dealing with a "well-involved" fire in a one-storey building, a Fenz spokesperson said.
An ambulance arrived to deal with one patient suffering from possible smoke inhalation.
There was a cloud of black smoke covering the main street of Oamaru.
It comes the day after a Dunedin Indian restaurant was damaged in a similar fire.