Video report by ITV News Business and Economics Editor Joel Hills
The Office for National Statistics said economic activity dropped by 20.4 per cent in April - the largest drop in a single month since records began in 1997.
The fall massively outstrips the then-record 5.8 per cent drop in March gross domestic product (GDP) that the ONS reported last month.
It means that GDP fell by 10.4 per cent in the three months to April and sets the UK on course for one of its worst quarters in history.
Speaking following the release of the figures, Mr Johnson said he was "not surprised" the UK had been "badly hit" by the lockdown.
Boris Johnson says country will 'bounce back' from lockdown economy hit
The prime minister added: "One of the things the UK has got right is the way we've tried to handle the situation with the furlough scheme and many other schemes we've put in place.
"What I want to do now is work slowly to get the economy back on its feet... I think slowly confidence will return and you will see a bounce back."
He reiterated his general election promise to "level up" the country, in education, services and transport infrastructure, and more plans would be announced in the coming weeks.
"We're going to be doubling-down on our agenda of uniting and leveling up. Infrastructure, technology, investment in our future, building the platform that business needs for growth," he said.
ITV News Business and Economics Editor Joel Hills explains impact of GDP fall figures
Large parts of the British economy were placed on ice on March 23 when Prime Minister Boris Johnson told people they must stay inside and only leave the house when absolutely necessary.
The measures were announced to slow the spread of Covid-19.
The figures are worse than what some experts predicted. A consensus compiled by Pantheon Macroeconomics suggested there would be a 18.7 per cent drop in GDP.
May’s GDP figures are also likely to be hard hit, before things start to ease again in June as the economy slowly reopens.
How the UK economy has shrunk
Health minister Edward Argar said: "That's clearly a significant contraction. It's something I know the Chancellor was aware was likely to happen given the impact of lockdown and restrictions on businesses and individuals.
"But it is nonetheless a signicant contraction which is why we've put in place one of the most generous schemes in the world of support for individuals and businesses.
"But we also need to in careful, measured ways, to reopen the economy and get the country working again."
'We need to be careful and reopen the economy to get the country working again': Health minister Edward Argar
Shadow Chancellor Anneliese Dodds said: "What particularly concerns me is that actually we're not just looking at one month of economic damage.
"There was a report that came out a couple of days ago from the OECD and it suggested that the drop in GDP for this year for the UK would actually be worse than for every other industrialised nation.
"So we're in a very, very difficult situation as a country and we will need strong action to help us climb out of this as quickly as possible."
'We need strong action': Shadow Chancellor Anneliese Dodds
Former Chancellor Ken Clarke said he had "sympathy" for the Government and that the majority of the next parliament would be focused on bringing economic prosperity back to the UK.
"We're in the middle of theworst recession in the lifetime of anyone living.
It's quite different to any previous recession we've had, we have little to go on. We haven't had a plague causing the economy to stop before so this is a very grave crisis.
"I think we all realise that April was going to show up just how bad it was."
He added: "I think most of the rest of this parliament is going to be taken up with this struggle to get the economy back to decent health.
"The idea we're going to have a quick bounce back, I personally would be very, very surprised if that were to happen."
Ken Clarke doubts fast UK economy bounce back
Neil Birrell, chief investment officer at asset manager Premier Miton, said: "All the economic data out of the UK for April showed the economy to be in awful shape - in fact, worse than expected.
"Other countries' data is improving as lockdown eases and the concern is that the UK is getting left behind and, as we are currently witnessing, equity markets are very sensitive to any threat to recovery."
ITV News Business and Economics Editor Joel Hills said the downturn was "unprecedented" and that the UK had "never seen anything like this".
ITV News Political Correspondent Paul Brand tweeted: "Covid-19 has hit the UK hard - one of the worst death rates in the world and now one of the worst economic downturns."
Jonathan Athow, deputy national statistician at the ONS, told BBC Radio 4's Today programme that prior to lockdown, the biggest fall they had seen in a single month was two per cent.
"If you take March and April together the fall was 25 per cent. So in two months the economy shrank by a quarter," he said.
Mr Athow added that "virtually every sector has been shrinking" but said April was "likely" to be the "low point of economic output".
He added: "It is really too early to know how quickly economic activity will recover in the coming months."
Attention is beginning to turn to how businesses will get back on track while still trying to limit the spread of Covid-19.
Tej Parikh, chief economist at the Institute of Directors, said many businesses will still need support as lockdown slowly lifts."Emergency loan schemes have helped stop firms collapsing, but left many saddled with debt," he said.
"Businesses will be reluctant to hire and spend on new projects as they repair their finances, particularly as social distancing eats into demand and productivity. Firms will continue to face cashflow challenges in the months ahead."
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