A top Ministry of Public Health official on Monday said that quarantine alone will not keep the country safe.

Dr Sophon Iamsirithavorn, director of the ministry's Communicable Diseases Division, told media on Monday that infected people will still cross the border no matter how stringent isolation measures for arrivals are.

"The most recent Covid-19 cases in Thailand were among returnees who appear to have been asymptomatic for long periods of time, possibly even the duration of their quarantine," said Dr Sophon.

The department has raised its alert level after two particular cases -- the first a French woman who tested positive a week after leaving quarantine and the second an Indian restaurateur living in Krabi who returned in February.

The doctor urged the public to maintain all health and safety practices adopted at the height of the domestic Covid-19 infection period.

Meanwhile, Dr Supakij Sirilak, acting chief of the Department of Medical Sciences, said the test result for the wife of the Indian restaurateur will be known today as efforts continue to trace any potential lines of infection in Krabi, Phuket, Chiang Mai and Sukhothai, all of which the man had visited recently.

Authorities in Sukhothai on Monday revealed the patient's timeline when he was visiting the province and said he had come into close contact with 32 people during his one-day stay.

Low-risk contacts were advised to observe social distancing and, where possible, self-isolate until doctors give them the all-clear.