The 548 new cases, most of them linked to a wholesale seafood market on the outskirts of Bangkok, come after Thailand saw only a small number of infections over the past several months due to strict border and quarantine controls.
Health officials said on Sunday (Dec 20) the new cases are mostly migrant workers from Myanmar connected to the outbreak at the Klang Koong shrimp market in Samut Sakhon province.
All of them were tied to a 67-year-old seafood vendor who tested positive for the coronavirus earlier, the director-general of the Department of Medical Sciences, Opas Karnkawinpong, said in a news conference broadcast to all TV channels on Saturday night.
The first case at the market was confirmed on Thursday, followed by 13 more on Friday.
"While there is a likelihood of finding more infections in crowded foreign communities around the shrimp market, they are low-risk groups because they are working age and healthy," Opas said.
He said most of those who tested positive were asymptomatic.
Samut Sakhon Gov. Veerasak Vichitsangsri said late Saturday that strict measures, including a 10pm-5am curfew and other travel restrictions, will be taken in the province to combat the outbreak.
The restrictions will be in effect until Jan 3.
Samut Sakhon is 34 kilometers (21 miles) southwest of Bangkok, the capital.
With fewer than 5,000 cases and 60 deaths, Thailand has been able to control the virus.
Prior to this week's outbreak, there had been very few cases of local transmission and life was mostly back to normal. - AP