Of the total, 6,044 were locals who tested positive when they went to hospitals for a check-up, 2,515 were found during proactive testing, 73 infections were found in prisons, and 24 were travellers from abroad.
Bangkok led the list of most cases with 2,399, followed by Samut Sakhon (591), Samut Prakan (405), Chonburi (399), Pathum Thani (397), Nakhon Pathom (315) and Nonthaburi (313).
Meanwhile, 3,687 patients have recovered and been discharged in the last 24 hours.
Of the total 345,027 cases so far, 251,658 have recovered and been discharged, 50,578 patients are still in hospitals, and 2,791 have died.
According to Worldometer, as of 11am on Monday, the number of confirmed cases globally had risen to 187.63 million, 171.58 million of whom have recovered, 11.98 million are active cases (78,292 in severe condition) and 4.04 million have died (up by 6,324).
Thailand ranks 60th on the global list of most cases, which is topped by the US with 34.73 million, followed by India 30.87 million, Brazil 19.08 million, France 5.81 million, and Russia 5.78 million.
Meanwhile, another 87,809 people were given their first Covid-19 shot in the last 24 hours, while 12,216 people were given their second shot, bringing the total number of Covid-19 vaccine doses administered in Thailand to 12,569,213.