TAIPEI - Two people had tested positive for the COVID-19 shortly after leaving Taiwan, the island's epidemic monitoring agency said on Wednesday.

The agency said it received notices from Vietnam and Japan about the two cases and have started to investigate.

The Japan case, a Taiwan resident, had returned to Taiwan from Japan in March and went back to Japan on Aug 31. He tested positive upon his arrival at the airport, according to the agency.

The Vietnam case, a Vietnamese woman who returned to her hometown from Taiwan on Aug 7, tested negative in the first two tests on Aug 7 and Aug 14 and turned positive in the third on Aug 26.

She was less likely to have contracted the virus in Taiwan, the agency said, adding that four people identified as her contacts in Taiwan tested negative for the virus.

Since the first case, a Japanese college student who tested positive for the virus shortly after leaving Taiwan in June, the island has received reports of 13 similar cases.

Except for two cases who were confirmed to have contracted the virus elsewhere, 11 remained unclear about the source of their infection and could not be ruled out being infected in Taiwan.

The agency also announced that an Indonesian man tested positive for the virus in Taiwan on Wednesday, raising the total number of COVID-19 cases in Taiwan to 489.