Forest parks have been closed to the public, just days after parking charges were waived to give people greater access to them during the coronavirus outbreak.
Department of Agriculture, Environment and Rural Afairs (Daera) Minister Edwin Poots said it was necessary after social distancing advice was ignored.
There had been a surge in visitor numbers over the weekend.
Some locations were "packed to capacity", he said.
On government advice, Mr Poots said the car parks would now be closed and he was urging people not to visit on foot.
“These unprecedented moves are to save lives," he said.
"I realise this is a disappointing decision, especially to families with children out of school and others using the facilities for physical and mental health reasons," Mr Poots added.
At the weekend, the department announced it was temporarily waiving parking charges at its public spaces so that people could use them to exercise during the restrictions.
But Mr Poots said that instead of safe wide-open spaces being available to people, there had been a huge rise in footfall with people failing to keep themselves and others safe from the coronavirus.
Mr Poots said that could not continue, so he was closing car parks and stopping public access to parks, forests and nature reserves, "where possible".
He said he was also urging people not to come on foot, but rather to stay at home.
The National Trust made a similar decision. Having initially said its gardens and car parks at other outdoor locations would be free, it later said they would be shutting after large numbers visited.
We're closing all our car parks, to further attempt to help restrict the spread of coronavirus. We encourage everyone to observe social distancing and not travel: https://t.co/YWk8TQLXOb pic.twitter.com/Ce33jbbPOl— National Trust (@nationaltrust) March 23, 2020
Parks in many council areas have also closed.
The government's social distancing guidelines say people are still allowed to exercise outside- either alone or with one other person who they live with - but they must keep a distance of at least 2m from others.