Schools are to close across Northern Ireland from Monday in a bid to delay the spread of coronavirus.
And officials said they could be shuttered until this summer.
Stormont First Minister Arlene Foster said “The societal and economic impact of this measure will be enormous.”
She said the closures were “unplanned and long-term”.
“This is unprecedented,” she added.
Ms Foster and Deputy First Minister Michelle O’Neill made the announcement in Belfast.
They had been at loggerheads after the Sinn Fein leader wanted to act sooner following a similar move from the Irish Republic.
The five main teaching unions have written to Stormont Education Minister Peter Weir asking him to set a date for closures.
In the Irish Republic, schools have been closed since Friday.
Mrs Foster said: “We have agreed that all schools will close to pupils from Monday March 23.
“The societal and economic impact of this measure will be enormous as parents have to adjust their routines to deal with this unplanned, long-term closure.
“Our medical advice was to delay this step for as long as possible as the closure will likely take us beyond the natural break for the summer.
“This is unprecedented.”
She said she was exploring how schools can continue to be a base for the education of children whose parents are health service staff or key workers like the emergency services.
The DUP leader added: “Educating our children cannot cease and remote learning and home packs for self-study are already being explored over the period ahead.”
The Irish National Teachers’ Organisation (INTO) union said it ended the uncertainty.
Northern Ireland Secretary Gerry Murphy said teachers will follow reasonable instruction from their school principals on managing distance learning of pupils.
He added: “This is a worrying time for all concerned but today’s decision will go some way to reducing the additional stress levels principals, teachers, parents, children and young people have been enduring over the last week.”
Six new cases of the virus were confirmed in Northern Ireland on Wednesday, bringing the total to 68.
It is not yet clear if private and voluntary nurseries would also close, while no announcement has yet been made about Further Education colleges.
More than 30,000 businesses are to benefit from official assistance worth £370 million.
Many workers have been laid off and pubs forced to close following warnings about social distancing.
An official rescue package will include a grant scheme worth £10,000 each for around 27,000 small businesses and a payment of £25,000 to around 4,000 firms involved in retail, tourism and hospitality.