Leeds is likely to face new restrictions from midnight in the fight against Covid-19, including a ban on households mixing in private homes.
Leeds City Council leader Judith Blake said she expected the city will be made an "area of intervention", while the leader for public health said the restrictions could last through winter.
Ms Blake told reporters: "We expect them to come in from midnight."
The addition of Leeds' population would take the number of people living under local restrictions to more than 16.2 million people across the UK.
Tom Riordan, chief executive of Leeds City Council, said: "What we are trying to do is give a simple message – you shouldn't really mix with other households."
He said about 780,000 people will come under the new measures which could be in place through the winter.
Mr Riordan added: "I think we know from the experience of Leicester, Greater Manchester and West Yorkshire that when these restrictions are brought in they do not tend to be lifted after a week or two."
Leeds director of public health Victoria Eaton said the city's virus rate was 98.5 per 100,000 people with a positive testing rate of 8.4%.
She said: "The spread of the virus is very dynamic across the city.
"It's clear to see we have very widespread community transmissions right across the city."
Ms Eaton said there were "high rates in some of our student areas" but said cases were rising in all age groups, not just young adults.
She said compliance with self-isolation rules was still low in Leeds.
"We want to find ways to support local people to isolate," she said.
"The expectation is the restrictions will be in place for a longer period of time, potentially right through the winter."
Speaking at a virtual news conference, Mr Riordan said the fine details of the restrictions had not been agreed with the Government yet, but the council wanted to let people know what was likely to come in at midnight.
He said it was expected that it would become law that households should not mix inside or in the garden, and that in pubs, restaurants and in public spaces, it would be strong advice that that should not happen.
Meanwhile, London is being made an "area of concern", according to London Councils, a cross-party organisation which represents all 32 boroughs and the City of London.
No additional measures will be taken in the city but testing capacity will be boosted to closely monitor the growth of the virus.
In a statement, London Councils urged residents to follow the new Government restrictions introduced on Thursday and said rising cases were a "stark reminder that now is time for all Londoners to pull together and take action to keep themselves, their families and their communities safe, and to ensure that London's economy is protected".
It added: "London boroughs are working with their communities, business and the police to engage, educate, explain and, if necessary, enforce the new restrictions and regulations, and the Government must ensure that it funds these so resources do not need to be drawn from other services.
"We ask all Londoners to work together and abide by the national restrictions announced on Tuesday."
Many parents and carers are worried about the impact COVID-19 measures are having on their children
Support is available to help you talk about these worries with your family and stay connected with them. https://t.co/Jq7FRsnhN3
— Public Health Wales (@PublicHealthW) September 25, 2020
In Wales, Cardiff and Swansea will go into local lockdown from 6pm on Sunday, the Welsh Government confirmed.
Under the restrictions, people will not be able to enter or leave the areas without a reasonable excuse.
They will not be able to meet indoors with anyone they do not live with, with extended households suspended.
People must work from home when possible, health minister Vaughan Gething told a press conference in Cardiff.
The town of Llanelli will go into local lockdown on Saturday at 6pm.