At least one Thai soldier has been killed and four wounded in the fresh clashes that broke out around two areas in the easternmost province of Ubon Ratchathani
Thailand has since a year ago tightened visa processes and required all visitors and returning residents to undergo 14 days of quarantine in government-approved facilities.
Tourism a key source of income and jobs for Thailand. In 2019, it welcomed a record 39.9 million visitors who spent 1.91 trillion baht ($61.32 billion).
One million doses will arrive on May 6 and two million more are due by the end of May, said Witoon Danwiboon, head of the Government Pharmaceutical Organization (GPO).
Health authorities reported 1,583 new cases and 15 more deaths on Friday and said 250 patients were on ventilators.
Masks are widely worn in Thailand but the order to make them mandatory comes just a few days after Prime Minister Prayuth Chan-ocha was fined $190 for failing to wear one during a meeting.
* Parks, gyms, cinemas, bars, restaurants, day-care centres and schools have been closed in Bangkok, the outbreak epicentre, and non-essential travel from the capital is being discouraged.
The four million arrivals are expected in the second half of the year, Pipat Ratchakitprakarn told reporters, as the tourism-reliant nation prepares to reopen more broadly to visitors after more than a year of tight entry procedures.
"We have to divide up the areas based on seriousness, which is different and so measures have to be suitable for each area," Chawetsan told a briefing.
Activities involving over 50 people would be prohibited and 18 provinces, including Bangkok, classified as red zones and the remaining 59 provinces as orange.
