MOT tests for cars and light vehicles have been suspended across Northern Ireland after cracks were found in vehicle lifts.
Paul Duffy, chief executive of the Driver and Vehicle Agency (DVA), said late last night that the contractor responsible for repairing the lifts has "not provided sufficient assurance to DVA this evening on the effectiveness of the ongoing repairs".
He said tests had been suspended "to ensure the health and safety of staff and customers".
Motorists who booked their car for a test today have been warned not to attend the testing centre.
Mr Duffy said all customers due to have tests today, except those with four-year-old vehicles and taxis, will be automatically issued with an MOT exemption certificate and can continue to drive.
He said DVA will directly contact customers with four-year-old vehicles and taxis and are "working to urgently find a solution to get these vehicles through MOT".
"The DVA will issue a further statement as a matter of urgency to advise these customers and those who have MOTs booked for later this week," he said.
"We want to advise customers that more cancellations are very likely."
Tests on heavy goods vehicles and buses will continue as normal.
Mr Duffy apologised for the "considerable inconvenience and disruption this will cause for many people".
"Given the urgency of this situation, we are asking the public to follow media, social media channels and nidirect for updates.
Infrastructure minister Nichola Mallon has been informed and held an urgent meeting with officials last night.