The disease, which has killed just over 86,000 people in France since January 2020, shows no signs of abating despite the imposition of a nationwide curfew and a large take-up of staff using their computers at home to avoid travelling on public transport and going into the office.
The 20 zones include the Pas de Calais in the north, Paris and several of departments surrounding it as well as the Moselle in the east and the Var to the south.
Castex emerged from a meeting on Saturday with health minister Olivier Véran, interior minister Gérald Darmanin as well as leading health and security officials to demand more controls on people out on the street after the 6pm curfew.
He said he also wanted to see more efficiency from the vaccination campaign and checks on employers who are pressurising their staff not to work from home.
Castex reiterated his desire to avoid a broad-brush lockdown and keep restrictions local.
"The prefects are working hand in hand with local elected officials to strengthen our strategy to fight against Covid-19,” Castex said on social media.
"The question is not to be for or against containment but to do everything to avoid it," he also said.
La question n’est pas d’être pour ou contre le confinement mais de tout faire pour l’éviter.
— Jean Castex (@JeanCASTEX) February 27, 2021
Les préfets réunis en visioconférence ce matin travaillent main dans la main avec les élus locaux pour renforcer territoire par territoire notre stratégie de lutte contre la #COVID19. pic.twitter.com/ZM94HdvwyI
Castex’s call for a crackdown came as the northern city of Dunkirk entered a weekend lockdown.
The move followed infection rates rising above 900 per 100,000 people - nearly nine times the national average.
Similar to a lockdown imposed in the southern city of Nice, some 250,000 people in and around Dunkirk are only allowed to leave their homes for specific reasons.
The area’s 10 largest shopping centres are only open for click-and-collect services.
On Saturday, Nice’s assistant mayor, Anthony Borré, paid tribute on social media to the city’s residents for adhering to the lockdown.
Merci à l’immense majorité des Niçois et des Azuréens qui donnent une chance à ce #confinement en le respectant strictement.#Covid_19 pic.twitter.com/W3pM0YntVJ
— Anthony Borré (@anthony_borre) February 27, 2021
Borré also tweeted a TF1 report on the police's ability to use technology to track anyone trying to evade the rules.
📺 20h de #TF1 ce soir. pic.twitter.com/V4lgsnsDZ3
— Anthony Borré (@anthony_borre) February 26, 2021
In an interview with the magazine L'Express, Pierre Hurmic, the mayor of Bordeaux, said he wanted to take advantage of Castex's desire for regional flexibility and push back the city's curfew from 6 to 8pm.
"I am completely in favour of it," he told the magazine. "The state must trust the mayors. In Bordeaux, we are on a slightly downward plateau. We are less impacted than others. We can experiment."
