Eighteen Chinese nationals were arrested for illegal entry after they were found taking hiding out at a restaurant in Chiang Saen district of Chiang Rai on Tuesday.
Pol Lt Gen Sompong Chingduang, the commissioner of the Immigration Bureau, said his district office were tipped off about the illegal migrants that entered illegally into Thailand from Laos.
The Chinese nationals have been charged with illegal entry and defying the emergency decree on public health.
In Tak, meanwhile, police have arrested a man identified only as Chenathip and 30 Myanmar nationals at the natural border with Myanmar near the Moei River.
He told police that he drove his pickup truck to collect the Myanmar people from a pre-agreed point after being hired by a Thai man named Oun to take them to a central location in the province.
In Pattani, two Pakistani brothers, named only as Sami and Ikram, have been arrested on charges of illegally using Thai identification cards, illegal entry and working without permits.
Police said they received a tip-off that Sami was selling a variety of products and had been accused of persuading people to buy electrical appliances from him on credit.
Ikram, his elder brother, was also arrested for assisting his brother in the illegal acts.
Pol Lt Gen Chingduang said the bureau had also run a check on a Malaysian man, who recently returned home from Thailand and had since been found to have contracted COVID-19.
He said records confirmed the man had entered Thailand on 6th March, returned to Malaysia on 5th August and tested positive for the virus on 15th August 2020.
Officials are trying to pinpoint where the man visited before returning to Malaysia.