Checkpoints are being set up to restrict mobility in 13 provinces in a bid to prevent Covid-19 from spreading from the dark-red zone.

The checkpoints are being built and more security personnel would man all roads linking the 13 provinces with their neighbours from Monday, Taweesilp Visanuyothin, of the Centre for Covid-19 Situation Administration, said.

He warned of the difficulties people in the provinces would have if travelling. Travellers from other provinces to the dark-red zone would also be strictly screened.

Travel inside the 13 targeted provinces during the day, while still possible, was also discouraged and more checkpoints would be added, he said.

"Do not travel if not necessary," the CCSA spokesman said.

The newly designated dark-red zone consists of Bangkok and nearby provinces — Nakhon Pathom, Nonthaburi, Pathum Thani, Samut Prakan, Samut Sakhon, Chachoengsao, Chon Buri and Ayutthaya — and four southern provinces — Narathiwat, Pattani, Yala and Songkhla.

All but three have already been in lockdown since last Monday. Chon Buri, Chachoengsao and Ayutthaya, which were added to the zone on Sunday, will join them starting Tuesday.

A curfew from 9pm-4am is another restriction in these provinces.

Dr Taweesilp confirmed that domestic flights out of Suvarnabhumi and Don Mueang airports would stop from Wednesday.

The capacities of other public transport modes will be halved from Wednesday.