Police are investigating two incidents at service stations in the southern suburbs overnight.

About 11pm on Sunday 12 November, patrols were called to a service station on Goldsmith Drive at Noarlunga Centre after reports that a man armed with a machete had entered the store and demanded money from the till.

He left with an amount of cash and was last seen running towards the Colonnades shopping centre.

In the second incident, about 4.15am today (Monday 13 November), police were called to a service station on Dyson Road at Christies Beach after a staff member reported that a rock had been used to smash a window.

The same suspect from the robbery entered the store and stole money from the till before fleeing the scene.

No one was injured in either incident.

Anyone who may have witnessed either incident is asked to call Crime Stoppers on 1800 333 000, or online at www.crimestopperssa.com.au