Belgians must stay at home from midday on Wednesday until at least April 5 to prevent the spread of the coronavirus, Prime Minister Sophie Wilmes has said.
The only residents allowed out will be those needing medical attention, getting exercise or working in some businesses deemed essential, such as food markets and pharmacies, she said on Tuesday.
The tougher restrictions in Belgium follow similar measures in neighbouring France, as Europe grapples with the global outbreak that has killed more than 7,800 people.
Wilmes made her announcement just after taking part in a videoconference with the other 26 European Union leaders, during which they agreed to more fully coordinate further measures.
"Citizens are asked to stay at home in order to avoid most contacts, except for going to the doctor, to shop for food, the post office, a bank, pharmacy, petrol station or to help someone in need," she said.
Belgians can head outside for fresh air and brief exercise, but only alone or with someone they already live with, she added. Restaurants and bars have already been closed, but take-away deliveries continue.
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While supermarkets will remain open, shoppers should only be admitted if there is enough space for one person per 10 square metres, and they must not stay for more than 30 minutes.
Companies that can send employees to work from home should do so, and those that cannot should "scrupulously respect the rules of social distancing" in the workplace and on public transport, Wilmes said.
Businesses could be fined if they break the new rules, she warned.
Foreign travel that is not "indispensable" is banned until at least April 5.
Belgium, a country of 11.4 million people, has recorded 1,243 cases of the novel coronavirus strain, and 10 deaths.