Around 850,000 people in Madrid have been told to stay at home, as Spain battles a huge rise in coronavirus cases.
The restrictions on freedom of movement came into force in parts of the Spanish capital on Monday, with those affected only able to leave their neighbourhoods for basic necessities such as going to work, going to the doctor or taking their children to school.
Those in the affected areas represent 13 per cent of Madrid's population, the local government said. They also account for roughly 24 per cent of the cases detected in the last week.
It comes as the country's total number of cases increased by more than 14,000 on Friday with Spain seeing the largest outbreak in Europe in recent weeks.
The restrictions are in zones with more than 1,000 infections per 100,000 inhabitants, and will be in place for at least two weeks, the government said.
Spain's prime minister Pedro Sanchez said the restrictions will not extend to a return of the severe nationwide lockdown that was seen in March.
Hundreds of protesters gathered in several of Madrid's most deprived neighbourhoods on Sunday, many of them wearing masks, to protest the announcement of the new measures.
Many reportedly called on regional President Isabel Díaz Ayuso to step down over the regional government's decision.
In Vallecas, a district in the south of Madrid which has one of the highest infection rates, protesters chanted "Vallecas is not a ghetto" and carried placards decrying what they see as class-based segregation.
Now in an effort to contain the spread of the virus, Madrid will close parks and gardens in certain areas and while shops and restaurants will remain open, capacity will be limited.
Europe sees an alarming rise in cases
Infections in Europe are now higher than they were at the peak of the pandemic in March, due in part to increased testing.
Dr Hans Kluge, the World Health Organisation's regional director for Europe, has said he expects that deaths will rise in October.
"We have a very serious situation unfolding before us," said Dr Kluge last week.
Indeed, France, like Spain, has been struggling with rising case numbers and hospitalisations.
France recorded more than 13,000 new positive COVID-19 cases on Friday, a record in the country.
Several French cities are now issuing new restrictions with gatherings capped at 10 people in Marseille, Bordeaux, Lille and Nice. In Lyon, where there have been nearly 200 new cases per 100,000 people, local authorities are expected to follow suit by Monday.
France also recorded 123 deaths in a single day, a record high since May when the country was first coming out of lockdown and cases were decreasing.
The United Kingdom, which recorded more than 4,000 new cases in a single day, is also planning new restrictions.
Around 2 million people in the northeast will be subject to tighter restrictions and gatherings are limited to six people throughout England.
Transport Secretary Grant Shapps warned on Monday morning that a rise in deaths is expected to follow the recent rise in cases and hospitalisations.
“This is a tipping point, this is a very important moment," he told Sky News.
The UK's chief medical officer Chris Whitty and Chief Scientific Adviser to the government Sir Patrick Valance are to make a statement on Monday about the coronavirus situation in the country.