Earlier the city had limited gatherings to 30 people.
It has closed bars, dance clubs and karaoke parlors and banned festivals.
The city, a leading tourist destination and a coronavirus epicenter last year, has reported 112 Covid cases since May 4.
While authorities said the outbreak has been brought under control, mass testing is still being done to zero in on any potential source of infection.
In the latest wave that began on April 27 Vietnam has had 713 cases in 26 cities and provinces.