The website for booking new driving tests in England and Wales has crashed, after it re-launched 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.
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, 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.
Amy Hanley-McLean tweeted shortly that she had been trying to book a test all day.
"Got as far as choosing test centre only to see no availability at all at any of the test centres within 60 miles of me," she wrote.
"Then crashed again. Now all I am getting is 504 error!"
Louise Poyning described the booking process as an "absolute shambles".
"Okay, seven hours of refreshing and nearly four hours on hold is my limit," she tweeted.
The DVSA suspended all driving tests for up to three months from 20 March due to the coronavirus pandemic.
They have already restarted in England and Wales for people who had their tests cancelled because of the virus.
Tests are due to restart in Scotland on 14 September, but people in the nation are still unable to book a new driving test.
