Belgium closed all non-essential shops and banned homes from receiving visitors, except for a single "cuddle contact", as it announced its second coronavirus lockdown on Friday.
The country had the highest rate of infections in the EU as of Friday, according to the European Centre for Disease Prevention and Control.
Over the last fortnight there were 1,609 confirmed infections per 100,000 inhabitants – an increase of 186 per cent compared with the two weeks before.
Hotspots such as Spain and Italy have less than a third of that total. France, which reintroduced a full lockdown this week, has just 706 infections per 100,000 people.
Hospitals and experts had warned that, unless there was a drastic lockdown, Belgium's health system would soon face breaking point. The country's new rules take effect on Monday and will last until December 13.
"We are going back into a strict lockdown, which has only one purpose – to ensure that our healthcare system does not collapse," Alexander De Croo, the prime minister, said as he announced the measures, which build on existing rules including a midnight curfew and closed cafes.
Belgium's borders have not been closed, but travel is strongly discouraged. The country, however, will still allow people to travel to a hotel or secondary residence in the country. Working from home is mandatory where possible.
Mr de Croo said shops could still deliver and operate on a "click and collect" basis. Hairdressers and other contact professions such as masseuses must close, as well as theme parks and zoos.
The government said each home was only allowed one visitor, who must also be the designated "hug-buddy" for someone living alone. That person, known as a "knuffelcontact" in Dutch, is someone outside a household you can have close contact with.
The "cuddle contact" rule was introduced to safeguard the mental health of people living alone during lockdown. People living alone are allowed two "hug-buddies" under the new rules.
The new rules replace the "rule of four", which allowed for four members of a social bubble. Gatherings outside remain limited to four people, and attendances at funerals are limited to 15.
The one week half-term holidays, which started on Friday, will be extended for a week until November 15, and distance learning in higher education will continue until mid-December.
UK and EU negotiators are in Brussels for trade negotiations. They will discuss the new measures but talks are expected to continue as planned.