People travelling from tier-four areas to other parts of England are being asked to “assume” they have the new coronavirus variant and self-isolate.
Health officials said anyone who has come from a tier-four area or Wales to parts of the West Midlands and North West should stay at home for 10 days.
No visitors are allowed to a house where someone is isolating, even on Christmas Day, the statement said.
People who test negative are also being told to self-isolate.
Statements were issued by the Greater Manchester Combined Authority and the West Midlands Conurbation Local Resilience Forum, which said it applied to people travelling to the region on or since 18 December.
They said the new advice followed the emergence of the new variant of coronavirus, which had seen a “very rapid increase in cases in London and parts of the South East and East of England”.
“Although our region is not in tier four, rates are increasing and it is highly likely that the new variant is circulating,” the West Midlands statement said.
It also told people to change Christmas plans as much as possible and only to meet with those in their bubble.
“Other people who live in the house do not need to self-isolate unless they get symptoms but no visitors should be allowed in that house at all, even on Christmas Day.”
Dominic Harrison, director of public health for the Lancashire authority of Blackburn with Darwen, told BBC Lancashire that anyone who had travelled from a tier-four area since Wednesday should self-isolate for at least five days.
The guidance also calls on those who have symptoms to get tested and self-isolate for 10 days, without waiting for results.
Dr Jeanelle de Gruchy, the director of public health in Tameside, Greater Manchester, said the variant’s spread was “extremely worrying”.
Other parts of England, including Doncaster and Telford, have issued similar guidance.
Wales entered lockdown on Sunday, with new restrictions covering the Christmas period. Hundreds of people are thought to have contracted the new variant, First Minister Mark Drakeford said.
Kathryn Stanczyszyn, BBC Midlands
The rate of coronavirus hospital admissions in the West Midlands has been among the highest in the country – and the last thing the region needs is a more transmissible strain on the rampage.
Public health bosses admit, though, it’s already here. Today’s message is about trying to mitigate the impact of that.
That message is basically that if you’ve come from a tier-four area in recent days, act like you’ve got the virus. And stay at home.
How far people will follow this is another matter. It’s not a legal requirement, but it’s been described to me as “the strongest possible advice”.
Of course Christmas plans are already in the balance for many. This is another blow, but one that it’s felt is entirely necessary as this Covid winter really kicks in.
Chief scientific adviser Sir Patrick Vallance, said public health directors in Greater Manchester and the West Midlands “need to make decisions” as they have a “role to make sure their local population is looked after” and they’re “doing a fantastic job.”
He also warned it was “likely measures will need to be increased in some places in due course.”
Much of the West Midlands and North West is in tier three, with Burnley in Lancashire having the highest rate of infection in the two areas, with 437.5 new cases per 100,000 people in the week up to 17 December.
Stoke-on-Trent has the highest rate of infection in the West Midlands, with 340.5 new infections.
Anyone arriving in the Liverpool city region has been told to get a coronavirus test, which is available in all six local authority areas.
If you live in a tier-four area, you must not leave or be outside of the place you are living unless you have a reasonable excuse.
You cannot meet other people indoors, including over the Christmas period, unless you live with them, or they are part of your support bubble.
Outdoors, you can only meet one person from another household. These rules will not be relaxed for Christmas for tier four – you cannot form a Christmas bubble in tier four.