Officers were called to the 7-Eleven store in the Klong Mudong area in Moo 6, Wichit, at 4:55am, reported Lt Col Narong Muangduang of the Wichit Police.
At the scene, police saw store staff Chutinan Thongkhao and Khantima Soda, who were still shaken by the robbery.
Ms Chutinan told police that a man entered the shop at 4:40am. He was wearing a red long-sleeved shirt, black jeans, a face helmet and a white face mask.
Ms Chutinan explained that while she and Khantima were standing behind the counter, the man carried a knife, jumped up the counter, came close to her and pushed her to stand close to Khantima.
The man ordered her to open a cash register, but she replied that she could not open it.
The man looked under the counter and found some cash placed on a drawer. He grabbed the money and calmly put it in his jean pockets. Then he jumped across the counter and walked out of the store.
Through CCTV footage, the man came and left the scene by riding a red unknown model motorbike towards the Muengthong-Khaokhad Rd.
The man made off with about B9,000 cash, police reported.
Police believe the robber may be the same man who robbed the 7-Eleven in Kalim on Nov 5, as he remains at large, Lt Col Narong noted.