The Public Health Ministry reported 89 new cases on Saturday in the largest daily jump since the coronavirus outbreak, bringing the total to 411.
Of the new cases, 51 were linked to existing patients.
Thirty-two people in Greater Bangkok and some provinces contracted the virus from people infected during a boxing match.
Two new patients linked to the cases involving an entertainment complex were reported in Ekkamai and Sukhumvit areas and they went to Chiang Rai province.
Six cases linked to a mosque in Malaysia were reported in Pattani, Narathiwat and Yala provinces
The remaining 38 new cases were not linked to the three incidents. Twelve came from abroad and several of them had gone to pubs. Six were drivers and 20 others are being investigated.
Of the accumulated total of 411 on Saturday, 366 remained hospitalised, 44 were discharged and one died.
The ministry said recent new cases are young people in the working age who were at risk because they still socialised normally and did not adopt social distancing.
It urged people to stay one metre away from others, skip social activities and non-essential travel, avoid crowded areas and work at home.
The officials also advised people who have been in high-risk places such as boxing stadiums, entertainment places, cock-fighting rings and theatres to self-isolate for 14 days. However, if they have no symptoms — fever, coughing, sore throat, runny nose, muscle pains — they need not be tested.
“Without the symptoms, the possibility of being tested positive is very low. Getting tested without the symptoms will therefore give people a false sense of security, leading to complacency,” they warned.