HANOI, Vietnam— Vietnam’s largest metropolis, Ho Chi Minh City, has begun a tightened lockdown to battle the coronavirus, a day ahead of U.S. Vice President Kamala Harris’s visit to the capital, Hanoi.

Police and army troops have mobilized to enforce the lockdown and deliver food and supplies to households. People in “high risk” districts must stay home under the stricter measures, imposed for at least two weeks.

The Health Ministry on Sunday reported 737 virus-related deaths, its highest single-day total. That raises the death toll since the pandemic began to 8,277. Hanoi is also under lockdown.

The U.S. has been Vietnam’s largest donor of vaccines, sending 5 million doses of Moderna. Separately, Vietnam has signed commercial agreements with U.S. vaccine makers Moderna and Pfizer to secure at least 80 million doses.

Last year Vietnam was praised for keeping the virus in check, an accomplishment generally attributed to the discipline of being a single-party communist state with tight controls at all levels.

But with the spread of the delta variant of the virus, the country is experiencing its worst outbreak by far, with more than half of the country’s 98 million population under lockdown orders.