Police are investigating a break and enter at a Port Macquarie discount appliance store, which would have netted the would-be thieves about 50 portable Global Positioning System (GPS) devices.

A security guard responded to an alarm at the Lake Rd premises about 1.15am on Wednesday.

The thieves smashed through a front plate-glass door to enter the premises.

The security guard chased the perpetrators to Fernhill Rd, where he lost sight of them.

A large white bag was found nearby.

The GPS units were recovered from the bag.

Police have seized the units for forensic examination as the investigation continues.