The Phan Thong Police Station was alerted to the robbery at 4am at the Family Mart shop in Ban Kao village, Tambon Nong Tamlueng.
Two staffers, Panawan Inang, 26, and Monthira Nikornkul, 21, told police that a tall man with a one-foot long knife walked into the shop wearing a flu mask and forced them into the toilet at the back of the shop.
They said the robber initially forced them to undress but they warned him that police were coming.
They said the man then rushed to the cash counter and grabbed Bt5,000 in 10-baht coins, Bt5,000 in 5-baht coins and Bt1,000 in one-baht coins and left.
Police have yet to check footage of security cameras to try to identify the robber.