Thais abroad who have booked flights back home risk being turned away at check-in if they cannot show a health certificate, which is difficult to get in many countries.

The Civil Aviation Authority of Thailand (CAAT) on Wednesday said that travellers from 11 more countries need to show health certificates before boarding flights to Thailand from Friday. The agency issued another annoucement on Thursday night applying to foreigners from all countries from Sunday.

Foreigners travelling to Thailand need verification of their travel history in the previous 14 days and a health certificate certifying they "pose no risk of being infected by the Coronavirus Disease (Covid-19)", issued no more than 72 hours prior to travel.

Also required is health insurance that covers Covid-19 treatment and shows minimum medical coverage of US$100,000 (about 3.2 million baht) in Thailand.

Thai nationals seeking a boarding pass must present a "fit-to-fly" health certificate and a certifying letter from a Thai embassy, Thai consulate office or the Thai Foreign Ministry.

Although Thai nationals require only the fit-to-fly certificate and not the Covid-19-free certificate to board, many are finding it difficult to meet the requirement, especially in Europe.

The Facebook page of the Thai embassy in London has been flooded by over 1,200 comments, mostly complaints and pleas for help.

Gail Powacht, 55, mother of a 20-year-old student in Plymouth, said her daughter had booked a Thai Airways International flight to Thailand on March 27.

"What are these requirements for? It's impossible to get only a health certificate. The requirement for the embassy letter is a double burden," she told the Bangkok Post, adding the embassy will not issue the letter unless a health certificate is presented first.

Foreign Ministry spokesman Cherdkiat Atthakor acknowledged that health certificates are unavailable in many European countries and that this problem has been raised at a meeting of state agencies.

Meanwhile, embassies will be in touch and provide help to Thai travellers, he said. It is unclear what kind of help can be offered especially if health services are already overwhelmed.

A high-ranking Thai diplomat in Europe who asked not to be named, told the Bangkok Post: "With measures like this, many Thais will be stranded abroad.