The move to place Suffolk into lockdown-style Tier 4 coronavirus measures from Boxing Day was "inevitable", leaders have said.
In a government briefing, health secretary and West Suffolk MP Matt Hancock announced Suffolk, along with the rest of East Anglia, will face the harshest restrictions as Covid-19 case numbers escalate.
The new rules come into effect at 00.01am on Boxing Day, with no change to the current measures for Christmas Day.
What does each tier mean? (1)
Suffolk has experienced a 96% rise in case numbers over the last week, with the county's infection rate at 188 cases per 100,000 people.
The rise in infections has been partly attributed to the discovery of a new strain of the virus, which government scientists believe is more contagious.
Suffolk health chiefs have previously identified the strain in the county.
Dr Dan Poulter, MP for Central Suffolk and North Ipswich, said the move to place Suffolk under harsher measures was "inevitable" in a bid to ensure the county's hospitals are not overwhelmed.
He said: "It struck me from the data that has emerged over the last seven to 10 days indicating a rapid rise in rates that it was inevitable we would end up in Tier 3 or 4.
"The most concerning factor is our hospital is now beginning to up with patients. These factors are very concerning from a health perspective.
"I was surprised there wasn't a decision to put Suffolk in Tier 3 a few days ago.
"It's disappointing for Suffolk, but it was important to take swift action. I think it's the right decision.
"It's important that we now support businesses through what is going to be a difficult period."
Tom Hunt, MP for Ipswich, added: "Clearly this new strain has changed things quite dramatically.
"This move hasn't really come as a surprise. I did believe it would be the direction of travel.
"Ultimately I believe this is necessary, as we've seen over the last month how quickly things can change.
"Though my concerns for the local economy are as strong as ever, I have a responsibility as MP to support measures that protect the vulnerable."
South Suffolk MP James Cartlidge said on Twitter he had been in contact with the trusts that manage Ipswich and West Suffolk hospitals prior to the announcement.
He added: "Moving Suffolk to Tier 4 will be a blow for many and nobody wants businesses to be forced to shut their doors.
"However, with infection spreading so rapidly locally due to the new Covid strain, and leading to sharp growth in hospital admissions, this step is necessary & proportionate."
Jo Churchill, Bury St Edmunds MP, said: "This decision was not taken lightly, but with the figures reading as they do, it is absolute necessary to help bring the numbers down and get the virus under control across the county.
"Our hospitals are also under enormous pressure, with both an influx of coronavirus patients and the pressure that winter usually brings to the NHS."
Matthew Hicks, leader of Suffolk County Council, said: "While it is not the news any of us wanted to hear, it comes as no surprise that Suffolk finds itself in Tier 4 given the rates of infection in recent days.
"The figures speak for themselves. This rise in cases, exacerbated by a more infectious variant, means increased pressure on the National Health Service and its partners, who are in the front line in the fight against Covid-19.
"We now must use this move into Tier 4 status as a spring-board from which to re-double our efforts in working together to bring rates down.
"This is our opportunity to halt the spread of the virus and enable us to move back into Tier 2."
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