Almost 200 new infections were reported on Sunday, the highest one-day jump to date with the government hinting at more stringent measures on the way as the number of accumulated infections is predicted to surpass 1,000 in the next seven days.
In the wake of the announcement of a Bangkok "soft lockdown", scores flocked to bus stations to leave the city and the country.
The number of Covid-19 cases rose to 599 with most of the new cases concentrated in Bangkok, said Public Health Ministry spokesman Thaveesilp Wisanuyothin. Dr Thaveesilp reported an increase of 188 new confirmed cases.
Shortly after Bangkok governor Aswin Kwanmuang ordered the closure for three weeks of shopping malls and markets except those selling food and essential consumer goods, five adjacent provinces of Samut Prakan, Samut Sakhon, Nakhon Pathom, Nonthaburi and Pathum Thani followed suit, triggering speculation that a full lockdown was coming.
Eighty thousand people boarded buses heading out of Bangkok on Sunday. Mostly migrant workers rushed to bordering provinces aiming to go home to neighbouring countries before the Thai borders close. At the same time, the Interior Ministry told provincial governors to keep an eye on people from Bangkok heading for their provinces amid fears they would further spread the disease.
Responding to speculation of a full lockdown, Deputy Prime Minister Wissanu Krea-ngam said on Saturday the government had considered several measures to tackle the spread of the novel coronavirus.
He said whether these measures would be implemented depended on an evolving situation but noted that people "would be given a heads-up". He said the lockdown was highly sensitive and would have adverse impacts.
"The government has thought about it and we're waiting for a signal from medical authorities," Mr Wissanu said. "The prime minister is listening to opinions of medical and public health experts.
"Still, the government will have to consider people's safety as well as their convenience."
Last week, the government postponed the Songkran holiday on April 13-15 to restrict movements as authorities emphasised the need for people to distance themselves from each other to slow the spread of the virus.
Following the closure orders by Bangkok and five other provinces, the national committee on communicable diseases has alerted provincial authorities to new arrivals and asked transport agencies to implement social distancing measures as people are expected to travel home.
In the letter to transport authorities, the national committee on communicable diseases stressed the need to screen passengers before boarding, to practise social distancing while away, and to clean and disinfect vehicles before and after the trips.
Transport officials have been instructed to obtain contact information from passengers too. Transport Minister Saksayam Chidchob said transport officials have been ordered to check the temperature of passengers.
Meanwhile, transfer of Covid-19 patients with mild symptoms from three hospitals to a new facility will begin on Monday, signalling that health authorities are prepared for a possible spike in infections.
Mahidol University council president Piyasakol Sakolsatayadorn said the transfer of mild cases to another facility is to make room for patients who may have severe symptoms. The former public health minster also indicated that a spike in cases is predicted in coming days.
Speaking at the daily news briefing on Sunday, Dr Thaveesilp said, of the rise in Covid-19 cases in Thailand, two groups were identified.
Of the first group of 65 cases, 21 were linked to the kickboxing cluster scattered in Bangkok, Loei, Nong Bua Lamphu, Udon Thani, Chon Buri, Phatthalung, Phra and Samut Prakan provinces; five related to entertainment venues; two associated with the religious activity in Malaysia, and 37 who were close contacts scattered in Bangkok, Samut Prakan, Sukhothai, Songkhla, Khon Kaen and Udon Thani.
The second group comprised 15 new cases; six Thai returnees and two foreign students from abroad, and seven working in crowded venues selling lotteries or goods at boxing stadiums.
The remaining cases were being investigated.
When asked if there would be additional measures to tackle the spread of the virus, Prime Minister Prayut Chan-o-cha said briefly: "We're working on it."