Several provincial governors have announced that people travelling from 28 red-zone provinces must be put into quarantine for 14 days.
Nakhon Ratchasima governor, Wichien Chantaranothai, said people from provinces declared by the Centre for Covid-19 Situation Administration (CCSA) as red zones must complete an entry request form and present a health certificate when arriving at his province.
They are also required contact public health authorities at their destination and remain in quarantine for 14 days.
Mr Wichien said the goal was to stem the latest surge of the novel coronavirus. The number of new infections in the province stood at seven, with no more new cases since the New Year.
Violators will be prosecuted in line with the Communicable Disease Act and subject to imprisonment and fines, according to the governor.
To be fully on guard, tough measures were needed, he said.
Nakhon Ratchasima has not ordered schools to close, but allowed them to close at their discretion.
Some private schools have postponed re-opening after the New Year holidays from Jan 5 to Jan 11, while they monitor the Covid-19 situation, he added.
Nakhon Ratchasima is classified as a "yellow zone" under "close surveillance".
In Ubon Ratchathani, provincial governor Sarit Withoon said two Covid-19 patients entered the province on Dec 25 and Jan 1 respectively.
One was a seafood vendor from Talat Thai Market in Samut Sakhon and the other a tourist from Nonthaburi.
People from some red zone provinces, including Samut Sakhon, Rayong, Samut Prakan, Chanthaburi, Chon Buri and three districts of Bangkok are required to contact local public health authorities immediately and isolate at home for 14 days. Violators will face penalties in line with the Communicable Disease Act and the Emergency Decree.
Ubon Ratchathani's Warin Chamrap and Na Tan districts where infections had been reported were declared areas under high surveillance. Places where many people gather are advised to close early.
Chai Nat governor Somboon Sirivej on Sunday signed an order declaring the entire province as a control area and requiring people from four red zone provinces to present a health certificate that proves negative Covid-19 results.
The health certificate must be issued no more than 72 hours prior to travel.
People in Chai Nat who travel to the four red zone provinces of Samut Sakhon, Nakhon Pathom, Rayong and Chon Buri are also required to be tested for Covid-19 and pay for the test themselves.
Violators are subject to imprisonment of up to two years and/or fine of up to 100,000 baht.
Private firms are also urged to come up with work from home arrangements for employees or stagger hours to reduce the risk of transmission.
