Starting from yesterday, applications can be made through a fully digital process completed at home without visiting a visa application center.

BN(O) status holders and their eligible family members who hold either a biometric BN(O), HKSAR or European Economic Area passport can submit their biometrics and verify their identity using the app.

"This process marks a major step forward in our move to digitize the UK's immigration system, with it allowing the first group of non-EEA nationals to complete the process of applying for a visa from home," UK's Future Borders and Immigration Minister Kevin Foster said.

Applicants would have to start their applications online at www.gov.uk before using the app "UK Immigration: ID Check."

When applicants reach the identity verification stage, they will be told to open the app. Those applying on a computer will need to scan a QR code or request a connection code from the website to connect the app.

When using the app, applicants will be asked to take a picture of their passport's photo page as well as scan their passport's chip using their phone by placing the phone on top of their passport.

Applicants are also required to scan their faces using their phone cameras, during which the screen will flash.

The app became the second most popular free app on Hong Kong's Apple's App Store yesterday, ranking just behind the LeaveHomeSafe app, which has been downloaded about 2.79 million times.

The UK government described the BN(O) Visa as "already a success," with thousands of people having applied since applications opened on January 31. It previously estimated the scheme would attract around 153,700 people in the first year and up to 322,400 in five years.

Although the specific number of applications will be published in May, British newspaper The Times reported nearly 5,000 Hongkongers have signed up for the new visa within two weeks.

"The commitment was made following the Chinese government's imposition of the national security law in Hong Kong last year, in breach of its commitments under international law," the UK Home Office said in its press release.

On Monday, British foreign minister Dominic Raab noted that the rights of Hongkongers are being systematically violated while addressing the UN Human Rights Council on current human rights situations in places including Myanmar and China.

"The national security law is a clear breach of the Sino-British Joint Declaration and is having a chilling effect on personal freedoms. Free and fair legislative elections must take place, with a range of opposition voices allowed to take part," Raab said.

Raab told UK political organization Conservative Friends of the Chinese on Friday that he has offered to visit Beijing and speak with Chinese Foreign Minister Wang Yi to ease tensions over Hong Kong, but China has not accepted his proposition.