It was also announced that healthy people returning from COVID-19 risk countries would now be quarantined at specific and guarded facilities.
Dr Suwannachai Wattanayingcharoenchai, director-general of the Disease Control Department, said one of the four new cases was an Italian, aged 29, who arrived from Italy on Sunday (Mar 1). He passed thermal screening at the airport, but the following day he sought treatment for a fever and cough at a private hospital.
He was then referred to Chon Buri Hospital in Chon Buri province.
The second new patient is a Thai man, aged 42. He arrived from Italy on Monday (Mar 2) and later sought treatment at a private hospital in Chon Buri for a fever, cough and sore throat. The two cases were not related.
The third is a Chinese student, aged 22. He arrived at Suvarnabhumi airport in Samut Prakan province from Iran on Sunday, intending to take a connecting flight. He had a fever, runny nose and a cough and was taken to the Bamrasnaradura Infectious Diseases Institute in Nonthaburi province.
The fourth is a Thai student, 20, who returned from Iran on Feb 27. He went to a hospital in Nakhon Si Thammarat province on Monday with a fever and runny nose.
The new cases raise the number of local COVID-19 cases to 47. Of these, 31 have recovered and returned home, 15 remained at hospitals and one died.
The Public Health Ministry also had 3,895 patients under investigation, of which 1,576 remained at hospitals.
Dr Suwannachai said that healthy people returning from COVID-19 risk countries would be quarantined at specific and guarded facilities. Previous returnees were being monitored.
Deputy Prime Minister Prawit Wongsuwon said five military compounds were prepared to quarantine Thai workers who would return from South Korea.
Defence Ministry spokesman Lt Gen Kongcheep Tantrawanit declined to elaborate on their locations, citing security reasons.