Thai authorities are implementing stricter border checks with neighbouring countries amid renewed Covid-19 fears.

Border police in Ranong province in the south of the country have round-the-clock checks on bridges and ports that have recently closed to limit the passages in and out of the country.

Thailand has seen a spike in Covid-19 cases over the last two weeks after Thai hookers who had been working at a Burmese brothel in Tachilek returned through an illegal border crossing.

Armed soldiers have been ordered to patrol the borders to prevent more cases.

In Tak province, where the Thai-Myanmar Friendship Bridge was built, borders have been closed since March.

However, Governor Pongrat Piromrat said the provincial communicable disease committee has allowed Thai nationals to return to the country since December 7 to deter illegal entry.

He said: "Thai nationals can come home, but only through the Friendship bridge. We are doing this to prevent them from breaking border protocol."

The strict measures followed a study that suggests Myanmar has a more infectious G614 strain of the virus than the D614 found in Western countries.

Sririraj Hospital's Dr Prasit Watanapa said the coronavirus strain found in Myanmar, formerly known as Burma, spreads faster than the virus from Wuhan, China.

He said: "60 per cent of Covid-19 infections in Myanmar were caused by the G614 strain. The strain that spread in Wuhan last year was called D614.

"G614, which can spread faster, therefore needs a faster response. Only one slip can cause great damage to the country."

Director-general of the Disease Control Department Opas Kankawinphong said they found 46 confirmed cases related to infected Thai returnees.

The agency has tested more than 5,000 people who came in contact with them but only one tested positive. All were taken to quarantine facilities and hospitals.

Thailand ranked highest in a global survey for its effective handling of Covid-19 and recovery from the crisis.