Authorities are stepping up disease control measures once again, as the nation gets ready for a possible new surge in Covid-19 cases.

A virologist has issued a warning that new infections could reach 30,000-50,000 per day if no measures are taken.

The Interior Ministry sent out a letter to all provincial governors ordering them to come up with a plan to slow the spread of Covid-19 in their areas and strictly enforce the rules, according to permanent secretary of the interior, Suttipong Juljarern.

He said provinces which are located next to other countries have also been told to heighten security along the border, to prevent illegal crossings of migrants.

In a Facebook post, the head of Chulalongkorn University's Centre of Excellence in Clinical Virology, Yong Poovorawan, said the region is experiencing an increase in Covid-19 cases.

"Covid-19 cases are also on an upward trend in Thailand and the country may see daily cases reach 30,000-50,000," Dr Yong said, noting that if positive results from antigen test kits (ATKs) are included in the figures, then Thailand's daily cases would have probably exceeded 25,000.

On Sunday, there were 8,814 positive ATK results.

Dr Yong urged asymptomatic people who test positive to urgently isolate without taking a RT-PCR test to confirm the infection.

The Public Health Ministry is planning to open more hotel isolation facilities and introduce the UCEP Plus programme, which would cover Covid patients with moderate and severe symptoms.

The head of the Faculty of Medicine at Siriraj Hospital on Sunday asked the public, especially those in at-risk groups, to immediately get a booster shot.

He said people may be able to enjoy this year's Songkran holiday if the national vaccination campaign is successful.

"This year's Songkran festival will be a test. If the number of cases reaches around 20,000 and vaccinations maintain their current pace, we may have to reconsider how much fun we can afford to have during the holidays," he said.