Liverpool's leaders have called on the government to impose a new nationwide lockdown to halt the spread of the new variant of Covid-19.
Acting mayor Wendy Simon and the city council's cabinet said urgent action is needed because the rise in coronavirus cases had reached "alarming levels".
They said it was "self-evident" the tier system has not curbed the variant.
It had been concentrated in London and south-east England but is believed to be spreading north.
Cases in Liverpool have almost trebled in the past two weeks to 350 per 100,000.
This is despite the city successfully leading the national pilot for community testing, which resulted in it becoming the first city to be taken out of tier 3 and moved into tier 2.
However, the recent rise in cases meant Liverpool returned to tier three on Thursday.
Speaking to the BBC News Channel, Ms Simon said: "I think the difficulty with this new strain of the virus is the speed at which it is infecting.
"What we have seen in these last weeks is that the tier system hasn't worked with this particular strain of the virus.
"The way the numbers are going, we're likely to go into tier four very, very quickly."
Ms Simon said officials wanted to "pre-empt that catastrophe" and "recover the economy quicker", adding: "We feel these three things - the mass vaccination, the mass testing and certainly a lockdown for a period - is what we need to get the city up and running again.
"There's a responsibility on us all to act promptly and bring it under control as soon as we can."
In an earlier statement, Ms Simon joined officials at the Labour-run city council to urge the government to "listen to those at the frontline, both in our hospitals and frontline services".
"We as a nation can cope with a lockdown," the statement said. "We have before and we can again."
The city's leaders also called for "an additional package of welfare and economic support" to address the "pain for our retail and hospitality sectors".
A further 57,725 confirmed cases were announced by the government on Saturday.
The sharp rise in numbers is partly down to a lag in reporting over the holiday period but, according to Public Health England, is "largely a reflection of a real increase".
Although the new variant is now spreading more rapidly than the original version, it is not believed to be more deadly.
On Sunday, the prime minister said regional restrictions in England were "probably about to get tougher".
He said possible changes included keeping schools closed, although this is not "something we want to do".
Boris Johnson said the government was "entirely reconciled to doing what it takes to get the virus down," and warned of a "tough period ahead".
He said increasing vaccination would provide a way out of restrictions and that he hoped "tens of millions" would be vaccinated in the next three months.