More than 300 migrant workers line up for Covid-19 tests in Chiang Mai province, northern Thailand, today (Dec 21) after an explosion of cases in the country.

Several districts in the northern province have been ordered to shut while health officials scan risky groups for the virus after finding more than 821 mostly migrant workers infected with the virus in Samut Sakhon province. There are connections through the track and trace system to the north.

Shocking footage taken from the market this morning shows how army chiefs have put up a ring of razor wire around the sprawling seafood market Samut Sakhon, which includes dormitories for the immigrant workers.

They are banned from leaving the compound and locals have had to deliver supplies of fresh food and water to them. There are believed to be more than 1,000 workers trapped inside the market area, which includes hundreds of shabby homes.

It came as several people in neighbouring areas tested positive following recent trips to the market, sparking fears of a second wave erupting in the country, which has largely kept the pandemic under control.

Deputy governor of the province, Surasak Polyangsong, said the first case was found last Thursday and since then, more than 2,000 people have been tested.

He said that an estimated 10,000 tests on people living and working in and around the market would be carried out using mobile labs this week.

Schools near Samut Sakhon have been ordered to shut while commuters between cities were advised to work from home. New Year events in the capital Bangkok have also been cancelled.

Thailand - which closed its borders in March and has enforced mask-wearing - has so far recorded 4,907 cases of coronavirus and 60 deaths.