First Minister Mark Drakeford says the Welsh Government is asking everyone to stay at home in a bid to contain coronavirus.
He was speaking after Prime Minister Boris Johnson announced a series of stricter measures aimed at tackling the coronavirus outbreak.
All high street shops will be closed except those selling food, pharmacies, banks and post offices.
Sixteen people have died in Wales after contracting Covid-19.
First Minister Mark Drakeford says there are 'big changes for us all' as tough new measures are announced pic.twitter.com/dXhIaND9Pa— BBC Wales News (@BBCWalesNews) March 23, 2020
Mr Drakeford's announcement is consistent with measures laid out by Mr Johnson and Scotland's First Minister, Nicola Sturgeon.
Mr Johnson said police will have the power to enforce the new rules, including the imposition of fines and dispersals of gatherings.
He said the restrictions would be reviewed in three weeks' time.
Public Health Wales announced a further four deaths related to coronavirus on Monday. The UK death toll has reached 335.
The first minister urged people to go out just once a day to shop for basic food and to exercise close to home.
All social events as well as gatherings of more than two people in public will be banned.
In a video statement, Mr Drakeford said: "Over the last few weeks we have asked everyone in Wales to make changes to the way we live our lives.
"We have asked you to stay at home, we have asked you to work from home if you can and not to travel unless it is absolutely necessary.
"We done this to slow the spread of coronavirus in Wales, to save lives and to protect our NHS.
"But now we have to introduce even more tighter measures."
What does it mean for you?
- All high street shops will be closed except a group of businesses such as those selling food, pharmacies, banks and post offices.
- Others allowed to open include newsagents, pet shops and vets, petrol stations, laundrettes and funeral homes
- Local NHS services including your GP will continue to be open.
- All social events, including weddings, baptisms and other ceremonies, as well as gatherings of more than two people in public should not take place.
- Funerals will continue to be held, but only with close family present.
The first minister added: "We are asking everyone to stay at home. Please only go out once a day to shop for basic food if you have to and to exercise close to home."
"Everyone should now also work from home, if you can.
"These are really big changes for all of us. We are making them because of the speed the virus is continuing to spread.
"Please help us to protect you and to save lives."
Although unprecedented in peacetime, these are necessary measures to supress the spread of the virus which is already threatening to overwhelm our NHS. This isn’t a national holiday. This is a national emergency. Each individual has a responsibility to follow the guidance.— Adam Price (@Adamprice) March 23, 2020
Plaid Cymru leader Adam Price said that although the measures were "unprecedented in peacetime", they were necessary to suppress the spread of the virus "which is already threatening to overwhelm our NHS".
"This isn't a national holiday. This is a national emergency. Each individual has a responsibility to follow the guidance," he said.
Cardiff North Labour MP Anna McMorrin said: "We all have a responsibility to halt the spread. This won't be easy, but a lockdown is the only way to save thousands of lives."
Former Welsh Secretary Stephen Crabb, MP for Preseli Pembrokeshire said it was "strange and difficult times for our country".
"We are all going to have show more patience, flexibility and kindness in our daily lives to get through this."
Paul Davies, Welsh Conservative assembly leader, added: "The Prime Minister's message couldn't be clearer. We are responsible for not just our own safety, but for everyone else's safety as well."