BEIJING — COVID-19 cases in the southwestern Chinese city of Ruili bordering on Myanmar have now topped 100.

That comes as authorities have launched an aggressive campaign to vaccinate all 300,000 residents of the city, whose outbreak is something of an anomaly in a country that appears to have all-but eliminated local transmission of the virus.

The National Health Commission reported an additional 20 cases on Monday, five of them in which the persons showed no symptoms.

The cases were detected during city-wide nucleic acid testing, bringing the city’s total to 51 confirmed cases and 56 asymptomatic cases, which China has placed in a separate category.

Confirmed cases are treated in hospital while those who test positive without showing symptoms are isolated and placed under isolation.

Ruili on Friday launched a five-day drive Friday to vaccinate its entire population, with state media showing people lining up to get the jab.

Some of those infected are Myanmar nationals and authorities have offered free vaccinations to foreigners living and working in the city.

Residents have been order to quarantine at home and non-essential businesses have been closed. Security measures have also been tightened along the porous border to prevent illegal crossings.