Tourists from everywhere are now welcome to visit Thailand, irrespective of their countries' Covid-19 situation, under a newly amended Special Tourist Visa (STV) long-stay programme.

However, these travellers still need to comply with Thailand's 14-day mandatory quarantine, deputy government spokeswoman Rachada Dhnadirek said on Tuesday.

The more liberal policy represents a government U-turn and is designed to help the ailing tourism industry.

STVs were previously only available to people from low risk-countries but that stringent condition was blamed for the low number of tourists taking advantage of the programme, with only 825 people from 29 countries and only six luxury yachts using it, said Ms Rachada.

The cabinet has also resolved to extend the stay period for yacht visitors holding an STV for another 30 days, or 60 days in total, she said.

Meanwhile, Prime Minister Prayut Chan-o-cha insisted on Tuesday that Thailand was not experiencing a second wave of the pandemic, nor dealing with any challenge of super-spreaders, as rumoured.

The truth was that a small group of infected Thais had illegally sneaked back into the country and visited places, which merely prompted routine checks as to whether they had infected anyone else, he said.

The PM urged people not to panic, saying that would only worsen the situation, and he cited the fact that a large number of hotel bookings had been cancelled in recent weeks due to an overreaction to media reports of a possible super-spreader.

Dr Chakrarat Pittayawonganon, of the Disease Control Department, meanwhile, revealed that among those now being treated for Covid-19 were four healthcare workers who were infected at alternative state quarantine facilities and private hospitals in Bangkok.

Their infections prompted an investigation as to how healthcare workers could have contracted the virus and whether it was their own fault or another cause, he said.

Health authorities on Tuesday recorded 19 new Covid-19 infections, one of which was a man in the northern province of Chiang Rai who thus became the 39th person to have caught the virus at an entertainment venue in the Burmese border town of Tachileik.

The Chiang Rai patient is the latest Thai national to catch Covid-19 abroad before sneaking back into the country illegally, said Dr Chakrarat, and was asymptomatic.

Meanwhile, Thammasat University has called off its 75th traditional football match with Chulalongkorn University, citing concerns over the pandemic.