More than one in five deaths in England and Wales is linked to coronavirus, figures show.
The Office for National Statistics said in the week ending 3 April the virus was cited on 3,475 death certificates.
It pushed the total number of deaths in that week to over 16,000 - a record high and 6,000 more than normal at this time of year when deaths tend to fall.
Meanwhile, Chancellor Rushi Sunak acknowledged there were "tough times" ahead economically.
It comes as the Office for Budget Responsibility, the UK's tax and spending watchdog, warned the pandemic could see the economy shrink by a record 35% by June.
Mr Sunak told No 10's daily coronavirus briefing that it was "clear" the situation could be "much worse" without the action taken so far.
But he admitted the government could not "protect every business or household" as it was clear coronavirus would have "serious implications".
And he said the economy would bounce back, adding the "single most important thing is to protect health of everyone".
Spike in deaths 'hugely significant'
The ONS report looked at the impact the numbers of people dying with coronavirus alongside all other deaths.
Normally at this time of year deaths drop because there is less flu circulating than there is in winter.
But instead it jumped up by to a record level of 16,000, the highest number seen since the ONS started publishing data in 2005, topping the biggest weekly toll during the 2015 flu outbreak.
ONS official Nick Stripe said it was clear the coronavirus pandemic had reversed that trend, saying the rising number of deaths was "hugely significant".
"This is not normal," he added.
'Never been as shocked'
But what is not clear is what else is contributing to this spike in deaths - the coronavirus cases contributed just over half of the "extra" 6,000 deaths.
It could be that cases of coronavirus are going undetected or other factors related to the lockdown and outbreak are having an impact, such as people not seeking treatment for other conditions or mental health deaths going up.
Prof Sir David Spiegelhalter, an expert in risk at the University of Cambridge, said this needed investigating.
But he said he had "never been as shocked" as when he saw the scale of the increase in deaths.
"I was upset. It is incredibly vivid. These are people," he said.
The ONS data lags behind the daily death figures reported by the government.
This is because it relies on death certificates, which are only often registered some days after the death, whereas the government figures are compiled from confirmed cases of deaths of patients who have tested positive for coronavirus, which can be gathered more quickly.
The government figures released on Tuesday revealed there had been another 778 deaths, bringing the total to 12,107 by 17:00 BST on Monday.
Another 5,252 people have tested positive for coronavirus, bringing the total number of cases to nearly 94,000 by 09:00 BST on Tuesday.
'My mother-in-law didn't deserve the death she had'
Edna Summerfield, 94, died earlier this month after testing positive for coronavirus. Her family believes she contracted it at her care home in Birmingham before she went into hospital on 7 April.
Her daughter-in-law Sylvia Summerfield said she feels people in care homes are being neglected - and called for PPE for care home staff as a matter of urgency.
"How many more elderly have got to die in care homes, infected by staff who don't know they have the virus?" she said.
"It is a very difficult time for us and I feel like people in care homes are being neglected.
"My mother in law didn't deserve the death she had. All the other residents are vulnerable in that care home now."
Deaths outside hospitals
The fact the government figures rely on deaths where a patient has tested positive - and in England and Northern Ireland this only covers hospital patients - has led to suggestions there has been an under-reporting of deaths in care homes and other community settings.
The ONS data does look at deaths elsewhere and shows that one in 10 coronavirus deaths this year have been in the community - half, just over 200, have been in care homes.
But care sector leaders are warning the true toll in care homes is much greater.
Age UK says the virus is "running wild" in care homes with Care England, the umbrella body for care homes, estimating there have been nearly 1,000 deaths.
If the reports are right it could be that there has been a spike in deaths over the past fortnight or that death certificates are not picking up all the cases.
The government confirmed there had been coronavirus outbreaks at more than 2,000 care homes in England - although they did not specify the number of deaths that had occurred.
Industry leaders from Age UK, Marie Curie, Care England, Independent Age and the Alzheimer's Society called for a daily update on the situation.
"The current figures are airbrushing older people out like they don't matter," Caroline Abrahams, of Age UK, said.
About 410,000 people live in care homes in the UK, living in 11,300 care homes for older people supplied by 5,500 different providers.
Mr Sunak told Tuesday's briefing that care home residents and workers had "absolutely not been forgotten".
Public Health England medical director Yvonne Doyle added that health bodies were aiming to have figures on coronavirus-related deaths in care homes published daily.
"In these very dispersed systems we just need to be absolutely clear that the cause of death that is attributed is correct, and that is what takes time on the death certificate to get right," she said.
In other developments:
- Women's fashion retailers Oasis and Warehouse were expected to appoint administrators, putting about 2,300 jobs at risk
- Scottish First Minister Nicola Sturgeon voiced her extreme concern over claims the NHS in England was being prioritised for personal protection equipment ahead of Scotland - but the claim was later dubbed "rubbish"
- A 99-year-old Army veteran raised more than £3m to help the NHS in the fight against Covid-19 and vowed to keep going even though he has smashed his original £1,000 target
- The friend of a nurse who died after contracting coronavirus said he "paid the ultimate price" due to a lack of personal protective equipment
- Many families of children eligible for free school meals said they were experiencing delays of up to a week for supermarket vouchers
- Austria and Italy became the latest European countries to begin easing lockdown restrictions