The Bangkok Metropolitan Administration (BMA) on Saturday ordered the immediate closure of Bang Khae Market after 80 people there tested positive for Covid-19.
The discovery renewed fears of a possible new cluster of infections as the country prepares to ease its coronavirus lockdown.
Parnrudee Manomaipiboon, director of the BMA's Public Health Department, confirmed that an active case search was conducted on Saturday at Bang Khae Market in Bang Khae district.
The search began at 9.30am with the testing of 1,400 people -- mostly visitors and vendors -- at Bang Khae and five nearby markets: Sirisetthnont Market, Kitti Market, Pasom Market, Wonder Market and Talat Mai Bang Khae Market.
Test results showed 80 were infected and the BMA is expected to continue its proactive testing initiative.
The BMA on Saturday sent swab samples to the official laboratory at the Ministry of Public Health for rechecking.
It has yet to ascertain the primary cause of the infections but the latest finding has renewed fears of a possible new cluster at the large market and surrounding communities.
Some people from outside the city visit the market and then return to their provinces.
People became concerned after the Nakhon Pathom Provincial Health Office posted an announcement calling on anyone who visited the market from Feb 27 to March 13 to urgently get tested for Covid-19 at state hospitals.
The announcement came after three people -- all from the same family -- tested positive for Covid-19.
A provincial health office official told the Bangkok Post that the main carrier was a 64-year-old mother who went to Bang Khae Market to buy ingredients for her somtam shop.
She also reportedly sold papaya salad at a shop on Phetkasem Road in Bangkok.