At least 33 children aged between three and six years old have tested positive for Covid-19 at a children's home in Thanyaburi district of Pathum Thani.
The new cluster to hit greater Bangkok was reported at the Rangsit Babies home, where six babysitters also tested positive.
It's suspected a driver working at the home was infected first and the disease spread from him, Dr Apisamai Srirangson, assistant spokeswoman of the Centre for Covid-19 Situation Administration (CCSA) said on Thursday.
Three new Covid-19 clusters were reported in inner Bangkok on Thursday taking the total number in the capital to 99, spread across 42 out of its 50 districts, she said.
Two were at a construction workers' camp on Soi Ramkhamhaeng 7 in Bang Kapi district, and the other was on Soi Silom 9 in Bang Rak district.
Dr Apisamai said 164 of 241 workers at the Bang Kapi site tested positive, while 126 of 257 workers at the Bang Rak camp were infected.
The third cluster was at a helmet-making company in Bang Khunthian district.
Officials found 165 workers out of 600 at the factory had contracted the coronavirus.
Dr Apisamai said the virus was first detected when an asymptomatic worker tested positive for Covid-19, before undergoing surgery.
Elsewhere, nine new Covid-19 cases were each reported at a tyre factory and a shrimp processing plant in Samut Sakhon.
Another 11 cases were reported found in a cluster at a processed sea weed factory in Nonthaburi.
Of 4,108 new Covid-19 cases reported over the past 24 hours, 3,865 were local infections and 14 imported cases.
Of the local infections, 2,835 were confirmed in hospitals and 1,030 via mass testing.
The 14 imported cases were from Cambodia (12 Thai returnees, two returning illegally), Oman and Somalia.
Bangkok again headed the top-10 infection list with 1,359 reported cases followed by Samut Prakan (297), Samut Sakhon (259), Chon Buri (254), Songkhla (216), Nonthaburi (170), Pathum Thani (157), Yala (119), Rayong (92) and Nakhon Pathom (91).
As of Wednesday, 39,517 people were receiving treatment in hospitals, with 1,564 reported to be critically ill and 445 dependent on ventilators.
In the vaccination drive, 172,903 people received their first dose on Thursday, while another 79,082 received their second jab. Since Feb 28, 8.4 million doses have been administered.
Global Covid-19 cases rose by 426,328 in 24 hours to 180.36 million on Thursday. The worldwide death toll went up by 8,516 to 3.91 million.
The United States had the most cases at 34.45 million, up 12,942. India was second with 30.08 million cases, up 54,319.