One week after the app was introduced, it pushed Facebook to the second spot on Apple Store in Vietnam and was in sixth place on Google Play on Friday.
On Monday, the app remains on top on Vietnam's Apple Store and has climbed to third place on Google Play.
The app was created by the Ministries of Information and Communications and Health for universal health declaration and disseminating information about the Covid-19 epidemic.
Both ministries encourage the public to download the app and provide information to support the health sector's efforts to control the epidemic.
The app asks users to provide personal and family information and contact details, and then take a disease survey and self-assess their personal health status and submit the answers.
While NCOVI is desgined for Vietnamese, the ministries introduced Vietnam Health Declaration app on both iOS and Android operating systems for foreigners.
The number of people suspected to have contracted the novel coronavirus in Vietnam was 102 on Monday, up from 97 on Sunday.
Besides quarantining them, authorities have also placed under medical observation many others who entered Vietnam from virus-hit areas or met infected people but do not show any symptoms.
Vietnam has so far recorded 57 cases, with 41 diagnosed since March 6, after going 22 days without a new case of infection.