The beach town and popular tourist destination of 500,000 has recorded 661 infections during the current wave.
Only emergency and anti-epidemic workers, reporters, sanitation workers, people repairing electricity, water and other infrastructure, drivers of vehicles transporting essential goods, and gas station and drug store employees are allowed to be on the streets during the night hours.
Others with permission to leave home for work after 7 p.m. must furnish a Covid-negative certificate.
Eleven communes and wards in Nha Trang deemed as high-risk areas have been locked down since Saturday.
Once a hotspot favored by Chinese and Russian tourists, Nha Trang began a 14-day social distancing campaign since July 9 under government Directive 16, which requires people to stay at home and only go out for necessities such as buying food or medicines or to work at factories or businesses that are allowed to open.
The lockdown was extended for two more weeks from July 23.
Khanh Hoa Province, home to the town, has had 1,375 cases so far.
Three months into its fourth wave, Vietnam has had 137,266 infections in 62 of its 63 cities and provinces.