The Interior Ministry has issued an order for people returning to the provinces during the current long weekend to be kept under quarantine for 14 days.
The order, intended to prevent Covid-19 transmission, was given in the wake of the exodus of people making trips upcountry mostly from Bangkok.
The Centre for Covid-19 Situation Administration (CCSA) earlier proposed the holidays -- Labour Day on Friday, Coronation Day tomorrow and Visakha Bucha Day on Wednesday -- be cancelled to keep people from travelling.
Medical experts voiced concerns over large numbers of people travelling around the country, but the cabinet shot down the idea.
The CCSA on Saturday said nearly a million people, many currently out of work due to the pandemic, travelled on Labour Day alone, which marked the start of the long weekend.
Permanent secretary for the interior Chatchai Promlert on Saturday signed an order for local authorities to ensure that visitors and natives who return from other provinces isolate themselves at home or at specific locations for 14 days.
It was reported on Saturday that a large portion of workers have left Phuket and headed home to other provinces. The popular resort island province, which is one of the coronavirus hotspots in the South, witnessed a long tailback of outbound traffic on Friday.
Phuket has recorded 220 coronavirus infections so far with two deaths.
Teera Warathanarat, an expert at the Faculty of Medicine, Chulalongkorn University, said the loosening of some lockdown measures and restrictions which triggered an exodus of travellers over the past few days could raise new infections.
Single-digit daily infections have been reported in the past several days including six each on Friday and on Saturday.
Similarly, Thanarak Plipat, deputy chief of the Department of Disease Control, said on Saturday that new infections appear to have been limited, but warned there remains a risk of the numbers increasing again.
"We need to put up a strong guard and keep it up," he said.