The NESDC also gave a cool forecast for the recovery, cutting its 2021 growth outlook to 1.5-2.5 percent, from its previous estimate of 2.5-3.5 percent.
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).
The ministry recorded 2,041 new COVID-19 cases, taking the country's total number to 71,025 since the pandemic began last year. The total number of fatalities now stands at 276.
"It's horrible this time round," said 39-year-old bus driver Chaowan Tessana, adding his work days had been halved from 15 days per month to six or seven.
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.
Anutin Charnvirankul told reporters the Food and Drug Administration (FDA) had approved the vaccine, in addition to those of AstraZeneca and Sinovac Biotech, which have already been administered in the country.
J&J's vaccine is called COVID Vaccine Janssen after the J&J unit that developed it.
8 Protesters also broke a traditional taboo by demanding reform of the powerful monarchy, saying the constitution drafted by the military after the 2014 coup gives the king too much power.
The new debt plan, which was increased from 1.465 trillion baht, also included borrowing for financing the budget deficit and state enterprise projects, Anucha Burapachaisri said in a statement.
The new debt plan will increase the country's public debt to gross domestic product (GDP) to 56.74% at the end of September, still below the 60% limit, Anucha said.
The committee felt the recovery could be impacted by rapid rises in the baht and would consider measures as necessary to ensure "exchange rate movements would not hinder the economic recovery".
The ministry slightly raised its 2021 forecast for exports, a key growth driver, to a 6.2% rise from the 6% increase it predicted in October, ministry spokeswoman Kulaya Tantitemit told a briefing.