The country reported 9,635 new cases, including 6,853 infections in prisons, according to the Center for COVID-19 Situation Administration (CCSA).
The new infections brought the country's total number of infections to 111,082, with more than 70 per cent of the infections having been confirmed since the beginning of April, when the third wave began and quickly spread across the country, reports Xinhua news agency.
The death toll climbed to 614, with 25 new fatalities reported on Monday, according to the CCSA.
The huge number of new infections came when the country decided to relax some restrictions on dine-in services at restaurants from Monday.
Restaurants in the capital Bangkok and three other provinces can provide dine-in services with limited serving capacity and operating hours.
Previously, they could only open for food delivery.