The emergence of the fake 100 baht bills follows reports and warnings of forged 500 and 1,000 baht notes found earlier there and in other provinces.
Pol Maj Gen Jeerawat Udomsud, chief of police in Trang, said on Thursday that since the discovery of 500 and 1,000 baht fake banknotes in Trang, forged bills of 100 baht denomination had started appearing there.
Two women grocery vendors who found them selves saddled with the fake 100 baht bills had already complained to local police in Muang Trang district - Patchanee Sukkhong, 37, and Sabai Satsen, 61.
The Trang police chief said the fake 100 baht bills had serial numbers beginning with 9A. The spread of fake notes in Trang was now a serious problem. Staff of the Bank of Thailand had been deployed in the province to monitor the situation and teach people how to detect the fake notes.
Pol Maj Gen Jeerawat said investigators had learned that the source of fake notes was a gang of 2-3 people who had passed counterfeit banknotes with face value totalling 4,000 to 10,000 baht in several areas.
They used them to buy goods at night, or at a time when the targeted sellers were busy.
Police were also looking into reports that counterfeit banknotes had also been found in cash withdrawn from banks, Pol Maj Gen Jeerawat said.