Campsites, caravan parks and tourist hotspots are to be closed in Wales by the Welsh Government.
First Minister Mark Drakeford confirmed he would shut the sites "to keep people safe and to reduce the pressure on our NHS".
Caravan and second home owners have been urged to stay at their main homes to not add pressure to rural services.
It comes after crowds headed to tourist hotspots at the weekend despite advice against non-essential travel.
Amid reports that some pubs are ignoring the ban introduced on Saturday, the Welsh Government warned those that continue to trade risk losing their licence.
Under the plans people camping or staying in caravans on holiday will be asked to return home from Monday.
'Bank holiday on steroids'
Routes to both Sugar Loaf and Pen-y-Fan mountains will be closed, and access to key hotspots such as Snowdon will be prevented.
The Welsh Government had faced calls to act after concerns mounted over the last few days.
A Snowdonia mountain rescue leader described the flood of people over the weekend as like a "bank holiday on steroids".
Chris Lloyd, of Ogwen Mountain Rescue Team spoke of the shock that so many should ignore official Coronavirus advice to stay away.
He added team members risked not only picking up the virus from those they saved but also from each other.
Mr Drakeford said: "Today, we are taking action to close caravan parks, campsites and some of our most recognisable visitor sites to keep people safe and to reduce the pressure on our NHS.
"My message is simple. Please stay at home and save lives."
Plaid Cymru leader Adam Price welcomed the decision, but he called for further action on holiday lets, other tourist accommodation and "non-primary residences". "Unless people cannot return home because someone is self-isolating in their primary residence, or for another humanitarian reason, all travel to non-primary residences should cease and people currently in non-primary residences should return home," he said.
Earlier, Education Minister Kirsty Williams confirmed to a news conference that Mr Drakeford had the powers to take action against caravan sites.
He had said the day before that he was awaiting advice as to whether he was able to force closures.
Ms Williams, a Liberal Democrat AM for the constituency of Brecon and Radnorshire, also said the gathering of crowds of people in Snowdonia and on Pen y Fan, as happened at the weekend, "cannot be repeated".
"These scenes have to come to an end," she said.
"I can tell you it is not essential to be in Pen y Fan this weekend or today," she added.