Coronavirus: Motorists 'turned back' at Irish border
People driving from NI into the Republic of Ireland are being turned back at the border if they do not have an essential reason for travel.
NI residents face fines from Monday if they are caught crossing the border without "a reasonable excuse".
The unprecedented step has been taken by the Irish government in a bid to prevent the spread of Covid-19.
Anyone engaged in cross-border travel in breach of Ireland's Covid-19 restrictions will be fined €100 (£88).
A number of Garda (Irish police) checkpoints were operational along the border from 07:00 local time.
At a checkpoint near Emyvale in County Monaghan, Insp Adrian Durcan said some people had "turned back" when requested.
"We have engaged with a few people who have not had essential reasons and on the advice of the guards, they have turned back," he said.
"I think it was three so far this morning."
Insp Durcan said fines would be issued to those not complying with the regulations.
"They will receive the fine and have 28 days to pay the fine, failure to pay that fine will result in a court appearance," he said.
"If they don't pay it we will issue a summons in respect of the offence and we will follow through on that summons."
Northern Ireland residents who have to cross the border for essential work or essential purposes, such as seeking medical treatment, will be exempt from fines.
Public health guidance in NI says people "should not travel in or out of Northern Ireland except where it is essential to do so".
The new rules are the latest in a series of decisions aimed at reducing travel to and within the Republic of Ireland, but it is the first time that people from Northern Ireland will face financial penalties for non-essential cross-border travel.
The Republic of Ireland is currently in the highest level of lockdown, known as "level five" in the government's five-stage plan for managing Covid-19.
Level five measures include a strict travel ban which means residents in the Republic of Ireland are temporarily prohibited from going more than 5km (3 miles) away from their home.
There are exceptions to the 5km limit for people who have to travel further for essential work; medical reasons; caring responsibilities; and other essential purposes such as shopping for necessities like food.
Since January 2021, gardaí have new enforcement powers which include the right to fine people engaged in non-essential travel.
Until now, Ireland's travel restrictions did not apply to people living in Northern Ireland, although Garda checkpoints a short distance from the border during earlier lockdowns did cause some tailbacks for cross-border traffic.
The new cross-border fines follow recent amendments to the Irish government's Covid-19 health legislation.
The regulations now state that "any other person who is not ordinarily resident in the state shall not travel within a relevant geographical location without reasonable excuse".
Gardaí said if they stop a car with a driver and two adults who should not be crossing the border, all three will receive a €100 fine. Cyclists and pedestrians will also be liable for fines.
"Travelling to an airport or port to take a holiday abroad is not an essential journey," they also warned.
Any adult who is detected travelling to an Irish airport or port for a non-essential trip or holiday abroad currently faces a €500 fine.
A Garda spokeswoman confirmed holidaymakers from Northern Ireland who are stopped by gardaÍ on their way to an airport will be liable for both that €500 fine and the €100 cross-border fine.