The website for booking new driving tests in England and Wales has crashed, after it relaunched on Friday morning following the coronavirus lockdown.
The Driver and Vehicle Standards Agency (DVSA) said it was aware some people could not complete their bookings amid "unprecedented demand", adding that it was working to fix the issue.
Driving test slots were open for booking from 08:00 BST.
Many people complained on social media about being unable to access the site.
"Coronavirus has severely impacted our business as usual operations, including by stopping driving tests for many months as part of social distancing," a spokesman for DVSA said.
"Following unprecedented demand for the driving test booking system after its reopening, we are aware that some users have not been able to complete their test bookings.
"We are urgently working to fix this and apologise for any inconvenience caused to those who have been unable to book so far."
There were limited numbers of tests available on Friday, but more will be released on Monday, the DVSA said.
Test slots are only available up to six weeks in advance - to allow the DVSA to react quickly to any changes in government guidance on coronavirus.
People have also been advised to check nearby alternative test centres for availability if they are unable to book a test at their preferred centre.
The DVSA suspended all driving tests for up to three months from 20 March.
They have already restarted in England and Wales for people who had their tests cancelled because of coronavirus, and will restart in Scotland on 14 September.
People in Scotland are still unable to book a new driving test.