A map has been published that shows where Leicester's localised lockdown will be in force.
The areas include Leicester city centre as well as suburban parts of Leicestershire, including Wigston, Oadby and Blaby.
Businesses within the boundary, such as non-essential shops, must remain closed for a further two weeks.
This means the city's bars, restaurants and hairdressers will not open on 4 July, unlike the rest of England. The relaxation of shielding planned for 6 July will also not go ahead.
Shops that were allowed to reopen on 15 June have to close as of today.
Schools will also close from 2 July, but will stay open for children of key workers and vulnerable children.
People are being urged to make essential journeys only and stay at home as much as they can.
The following areas in Blaby District are affected by the restrictions:
In Charnwood, the extended lockdown applies in:
Leicestershire County Council, which published the map, has said it is working on a postcode checker for those who are unsure about if their home falls within the red boundary line.
Leicester's mayor Sir Peter Soulsby said on Tuesday that the local authority and experts are still trying to work out where the virus is in the city.
He added: "We do still need to know more about where it is in the community.
"I've had lots of speculation and lots of questions about where it is in the community and we have not as yet been able to give satisfactory answers even to ourselves, no matter anybody else, about which parts of the community need the intervention.
"Which neighbourhoods, which communities, indeed which streets."
Council leader Nick Rushton said it was working with the government to help reduce the number of COVID-19 infections.
He said in a statement: "Clearly coronavirus does not adhere to lines on a map. And although county rates are below the national and regional averages, we can't be complacent and it makes sense to step up restrictions in areas closer to the city.
"This is the first localised lockdown on this scale and undoubtedly there will be issues to iron out. I understand this is disappointing news for residents, parents of schoolchildren and businesses when most of the country is opening back up but it's crucial that people follow the latest advice.
"Observing social distancing, handwashing, wearing a face mask where required and getting tested if you have symptoms remain vital.
"Our actions play a key role in shaping what happens next and I encourage people to heed the advice and play their part in helping to save lives and livelihoods."
Leicester currently has 135 cases per 100,000 people - three times the amount of infections in the next highest city.
A walk-in testing centre is being set up in the city for people with symptoms, with extra funding going to all Leicestershire councils to help support businesses and those forced to self-isolate.
On Monday night, Health Secretary Matt Hancock said the measures will be reviewed in two weeks and will not be in place "any longer than necessary".