Advice from the Northern Ireland executive states that anyone travelling to Northern Ireland from either Britain or the Republic of Ireland must isolate for 10 days.
This restriction was announced on a day when there were more than 21 Covid-19 deaths in Northern Ireland.
There have been 83 Covid-19 deaths in the past week and 57 the week before. With a hospital bed occupancy of 100% on Wednesday, 451 patients are receiving Covid-19 treatment in Northern Ireland with 31 in intensive care and 22 on ventilators.
Those who cross the border of Northern Ireland routinely for essential reasons will be exempt from the new restriction.