Stricter measures will be used to curb the spread of Covid-19 infections among migrant workers in Samut Sakhon after tests at seven factories over many weeks found almost 8,000 positive cases.

Surawit Sakdanupab, a deputy health official, said officials in Samut Sakhon had agreed to tough new disease control measures after news broke that the second wave of infections centred on the province is worse than first thought.

The "seal" method will apply to factories which have on-site accommodation -- workers will not be allowed to leave the premises.

The "bubble" strategy will apply to factories which have no on-site accommodation, so their workers stay at dormitories off the premises.

The goal of the new measures is to strictly regulate the travel and movement of workers all the way from their dormitories to their workplaces to prevent them from going to other locations, Dr Surawit said.

Officials may be deployed to watch the workers at their dormitories and deliver food and other essential items to them so they don't need go outside, he said.

Dr Surawit said the "seal and bubble" plan was likely to begin in the next few days.

He urged businesses to follow health safety protocol strictly and if possible to provide workers with accommodation inside their factories or at locations that were easy to control.

Dr Surawit said closing factories would be a last resort if they were confirmed to be the breeding ground of infections and could not be brought under control.

So far, testing has been conducted on 140,000 workers at 845 factories in Samut Sakhon.