Gardaí (Irish police) have started a major policing operation at the Irish border as part of the enforcement of new coronavirus regulations in the Republic of Ireland.
The action caused tailbacks on the Belfast to Dublin motorway on Thursday.
Drivers were stopped at a checkpoint at the Carrickdale roundabout where they were asked about their journey.
On Wednesday, the Irish government moved the country to the highest Level 5 restrictions.
The rules are to last for six weeks, but will be reviewed after four weeks.
People are asked to stay within 5km (3 miles) of their home, with exceptions for essential work and some other purposes.
Irish broadcaster RTÉ reported that 2,500 gardaí will be deployed across the country every day at 132 static and mobile checkpoints.
There will also be community patrols and support for the elderly and vulnerable.
Training has been suspended at the Garda college, with 260 trainees and their tutors among those being deployed.
Under new legislation, people who breach the Level 5 restrictions could face spot fines of up to €500 (£455).