Thailand confirmed six new cases of the new coronavirus on Tuesday, four of them Thai nationals and two Chinese, bringing the total to 25, the highest number outside China.
The four Thais included a couple who visited Japan and two drivers who picked up Chinese passengers in Thailand, Suwannachai Wattanayingcharoenchai, director-general of the Department of Disease Control, told reporters.
It was not clear whether the couple contracted the virus in Japan or after returning, Suwannachai said.
One of the infected Thai drivers, a 70-year-old, also had tuberculosis and was transferred into government care from a private hospital on Monday with worse condition than the others.
The other driver was tracked down by Thai authorities after being identified as one of the people in contact with an infected Chinese tourist, Suwannachai said.
Thailand confirmed its first case of human-to-human transmission on Friday when a taxi driver tested positive.
Thailand's total 25 cases consist of six Thais and 19 Chinese. Seventeen remain in hospital and eight have gone home, according to the health official.
Earlier on Tuesday, South Korea reported a 42-year-old woman has tested positive for coronavirus after visiting Thailand. It was not clear yet where she had contracted the virus.