Senior Sergeant Craig Dinnissen said a car was broken into a car park at Allans Beach at 10am. Two backpacks were stolen from the car and these contained the victims' passports and onward flight tickets.
A silver Holden Commodore had been seen acting suspiciously in the area, Snr Sgt Dinnissen said.
In a similar incident, another car was broken into at Moeraki Lookout on Tuesday about 3pm. A cellphone and wallet were stolen from the car which belonged to a workman who was working in the area.
Snr Sgt Dinnissen believed the thief was an "opportunist cruising the area".