Three more Thai returnees from entertainment places in Myanmar's border town of Tachilek were confirmed infected with Covid-19 on Thursday.
The Chiang Rai governor said two were women, aged 28 and 29, and one was a man, aged 33.
He said nobody had been in close contact with them.
Of the 37 Covid-19 cases in Chiang Rai, two had recovered and were discharged from hospital. Two more patients were expected to be released on Friday.
As of Wednesday, the number of Covid-19 cases coming from or related to Tachilek stood at 46. The new cases raised the number to 49.
Health authorities said the 1G1-7 hotel and entertainment complex in Tachilek, a hotspot of infection, was closed on Nov 24 and hundreds of Thais who worked there had to return home.
Many of them sneaked back across the border to Chiang Rai, dodging quarantine, and some of them travelled to other provinces.
