The NHS Covid Pass has crashed hours after the prime minister said it would become mandatory for some venues in England from next week.
Users reported being unable to download their domestic or travel passes from the NHS app and website following Boris Johnson's announcement.
People trying to access their pass on the app were met with a message asking them to try again later.
NHS Digital said the issue was being investigated as a priority.
From Wednesday, the NHS Covid Pass will be required to gain entry to:
- Nightclubs
- Indoor unseated venues with more than 500 people
- Unseated outdoor venues with more than 4,000 people
- Any venue with more than 10,000 people
The pass can be obtained by having two vaccines, a negative lateral flow test or a positive PCR test result in the past six months.
People will be exempt when attending religious worship, weddings and funerals.
Vaccine passports are already required for venues in Scotland, Wales and Northern Ireland.