The prime minister says 405,000 people have signed up to act as NHS volunteers in just 24 hours.
Speaking at the government's daily COVID-19 news conference, Boris Johnson said he wanted to offer a "special thank you to everyone who has now volunteered to help the NHS" following the launch of the scheme on Tuesday.
"When we launched the appeal last night, we hoped to get 250,000 volunteers over a few days," Mr Johnson said.
"But I can tell you that in just 24 hours, 405,000 people have responded to the call."
The PM said the volunteers would be "absolutely crucial" in the fight against the coronavirus.
He continued: "That is already, in one day, as many volunteers as the population of Coventry.
"And so to all of you, and to all the former NHS staff who are coming back now into the service, I say thank you on behalf of the entire country."
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The NHS has said the volunteers will support the 1.5 million vulnerable people who have been asked to "shield" themselves from COVID-19.
It comes as the UK spends a second day in lockdown over the coronavirus – and as the number of deaths was confirmed to have risen to 437 after further fatalities were in Scotland, Wales and Northern Ireland.
The PM said the country was coping "very well indeed" amidst the "most challenging possible circumstances".
Mr Johnson said that "never in our history has the government put its arms around people in the way we are doing now to help them get through this time".
He also said ministers would be examining legal ways of rallying against those profiteering by hiking up prices during the lockdown.
The government has said that a package of measures to support self-employed workers will be set out by the chancellor on Thursday.
Mr Johnson told MPs in the Commons earlier that the government would do "whatever we can" to support them.
The issue was one of a number raised during the final PMQs before the Commons breaks early for its Easter recess.
Mr Johnson also came under pressure over the official advice to the construction industry.
Construction workers can still go in as long as they can remain two metres (6.5ft) apart at all times, the government has said.
Amid reports of crowded Tube carriages in London, there have been calls for all non-emergency construction work to come to a halt in order to allow workers in that industry to stay home and avoid spreading the virus further.
London mayor Sadiq Khan has said "too many of the people using TfL services at the busiest times work in construction", as he reiterated his call for a ban on non-safety construction work.
Mr Johnson told MPs that it should be possible to "run a better Tube system" and implement a fuller service, as the row between the government and London mayor continued.
However, Mr Khan has insisted this is not possible due to staff being off sick or self-isolating because of the coronavirus.
Parliament is breaking up early because of fears over the spread of COVID-19.
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