More than half a million volunteers have signed up in just over 24 hours to help the NHS cope with the coronavirus outbreak.

The mass sign-up follows health secretary Matt Hancock’s call for 250,000 people to donate their time to help the 1.5 million people isolating for 12 weeks in an attempt to slow the spread of Covid-19.

Prime minister Boris Johnson offered a “special thank you” to the volunteers – who he said would be “absolutely crucial” in the fight against the illness.

Mr Hancock tweeted on Thursday: “NEWS: Fantastic that 560,000 people have now responded to our call to volunteer to support our NHS to defeat #Coronavirus.”

The army of volunteers will be delivering supplies, driving patients home from hospital and making regular phone calls to check in with vulnerable people who are isolating at home.

Health professionals and social care staff will be able to request help for at-risk patients via a call centre run by the Royal Voluntary Service (RVS), who will match people who need help with nearby volunteers.

The prime minister commended the 405,000 people who signed up within the first 24 hours during a daily Downing Street press conference on Wednesday.

He said: “They will be absolutely crucial in the fight against this virus. That is already, in one day, as many volunteers as the population of Coventry.

“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.”

Sir Simon Stevens, the chief executive of NHS England, praised the “overwhelming response” to the call for volunteers and thanked those who will devote their time to the health service.

He said: “Times like this show just how generous the British people are and how much they value our health service – we are blown away by this response and the kindness of our country.

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“I can’t thank those enough who have pledged to devote their time to helping others at what is a challenging and uncertain time for you and your families. The NHS is always there for you – now is your time to be there for us too.”

The appeal came after more than 1.5 million vulnerable people were told to stay inside for 12 weeks to shield them from the virus, including those with certain cancers and severe respiratory illnesses.

Shielding measures are being implemented to keep people safe and to ease the immense pressure on the NHS as medics battle to stem the tide of the coronavirus outbreak.

More than 11,700 retired doctors, nurses and health professionals have already returned to the NHS following a government appeal for medics to return to the front line.

In addition, 5,500 final-year medics and 18,700 final-year student nurses will begin working in the NHS next week.