Thailand's Health Ministry has reported 1940 new COVID-19 cases, while deaths have hit 21 for a second day, the highest daily number of fatalities since the pandemic began.
Thailand largely controlled the virus early in the pandemic through shutdowns and strict border controls. But a deadly third wave that began in early April includes the highly transmissible B.1.1.7 variant and has accounted for about half of its total cases and deaths.
Sunday's numbers brought the country's total confirmed infections since the pandemic began last year to 68,984.
Total deaths are now at 245. Thailand has vaccinated nearly 1.5 million people so far, mostly medical workers and vulnerable people, using imported doses of China's Sinovac and the AstraZeneca vaccines.
A mass vaccination program is to kick off in June with locally manufactured AstraZeneca doses.
Vaccine registration opened to the public this weekend with a goal of inoculating 70 per cent of adults in the country of more than 66 million people.