In an urgent message issued on Sunday, Mr. Chung urged authorities to closely monitor all people who returned from abroad and are living and working in the capital city. Suspected cases must undergo testing immediately.

The message requested people to wash their hands frequently and wear masks in crowded places.

Da Nang has put a halt to activities involving over 30 people and "non-essential" businesses, starting 1 p.m. Sunday, to contain the spread of COVID-19.