After 1,192 foreign workers got tested, 516 were found to be infected, accounting for 43 per cent infection rate.
Meanwhile, 32 more people were found to be infected after many people went to hospitals in the province for testing.
At 9pm on Saturday, Dr Opas Karnkawinpong, director-general of the Disease Control Department, held a press conference along with Pol Maj-General Thana Chuwong, Commander of the provincial Police Region 7, and provincial Governor Veerasak Vichitsaengsri.
The outbreak in the province follows a 67-year-old woman, who ran a prawn shop in a local fish market, testing positive on December 17 after experiencing symptoms on December 13.
Dr Opas said that after the case was detected, the Department of Disease Control, the Ministry of Public Health, together with the Samut Sakhon Provincial Communicable Diseases Committee and agencies in the area conducted hundreds of tests, after which 13 people, both Thais and foreigners, were found to be infected by noon on Saturday.
Further screening of 1,192 migrant workers, showed 516 of them, or 43 per cent, to be infected, Dr Opas said.
He added that the number increased to 548 after people visited hospitals in the province to be examined.
More than 90 per cent of the new cases were asymptomatic or have very few symptoms and most of them are foreign workers, he said.
After an assessment of the public health situation, Dr Opas said he believed the local health office would be able to cope with the situation through the cooperation of the people since most of the spread has occurred in a limited area without any severe cases. He said that although there was an increase among migrant communities surrounding the fish market, where they lived in crowded conditions, the group was at low risk of getting serious illness as they were in the working age group with strong health.
Governor Veerasak has decided to impose strict measures in the affected areas to control the spread of the disease for 14 days, from December 19 to January 3. Gambling establishments, tutoring institutes, sports schools and nurseries will be closed. Malls and convenience stores can open at restricted hours. They must not operate from 10pm to 5am. Fresh markets can open for six hours a day.