Millions of people lined in freezing temperatures to receive a second round of coronavirus tests in a city south of Beijing that is at the heart of China’s most serious recent outbreak of Covid-19, AP reports.

The National Health Commission announced that another 90 confirmed cases have been reported in Hebei province, whose capital Shijiazhuang has accounted for the vast majority of recent cases. Another 16 cases were reported in the northeastern province of Heilongjiang and one in the northern province of Shanxi.

All of Shijiazhuang’s roughly 10 million people have been ordered to undergo a second round of testing as authorities seek to isolate the sources of the outbreak. Some of the infections have been tentatively linked to wedding gatherings.