It comes after NHS England struck a deal with independent hospitals to provide 20,000 fully qualified staff and 8,000 more hospital beds.
The NHS will also have access to nearly 1,200 more ventilators facilities and other critical care facilities that have come under intense pressure as the coronavirus crisis intensifies.
Matt Hancock tweeted on Saturday night: "Delighted that 4,000 nurses and 500 doctors have signed up to return to the NHS in the first 48 hours of our call."
He said it was "brilliant support in our national effort" to tackle the virus.
In a video accompanying the post, he added: "But we need many more. It's easy to do, and we will make sure that your service is put to best effect.
"The whole country needs the NHS right now and if you're a retired doctor or a retired nurse then your NHS needs you."
Earlier this week, up to 65,000 former doctors and nurses were asked to answer the call to return to work.
Hundreds of new cases are being confirmed in the UK each day - with an additional 1,035 in the latest 24-hour figures, bringing the total to 5,018 in the biggest daily rise yet.
Meanwhile, Jeremy Corbyn has urged the government to go further to ensure economic security for those affected by the coronavirus pandemic.
In a letter to Boris Johnson, he welcomed Chancellor Rishi Sunak's plans to underwrite the wages of millions of workers who would have otherwise lost their jobs, but said the government needed to extend that support to cover the five million self-employed.
The Labour leader also called for protection for workers from losing their jobs, more support for renters, improved social security, and an increase in statutory sick pay.
He added that Labour would continue to work "constructively" with the government and that its proposals were intended to strengthen its response to the crisis.
He wrote: "We welcome the direction of the chancellor's announcements. But we continue to have concerns that the plans do not provide the economic security that everyone needs to be able to take precautionary measures in response to the coronavirus pandemic."
The number of people who have died after testing positive for COVID-19 in the UK reached 233 on Saturday.
A 41-year-old patient is thought to be the youngest UK victim since the outbreak began.
NHS England said all 53 whose deaths were announced in England on Saturday had underlying health conditions and the eldest was 94.
The number of deaths in Wales has risen to five, while Scotland now stands at seven and Northern Ireland's remains at one.
The new figures came as Environment Secretary George Eustice said there was no shortage of food in the country amid the coronavirus pandemic, with manufacturers having increased production by 50%.
At the daily Downing Street press conference, NHS England national medical director Stephen Powis said crisis panic buyers "should be ashamed" for causing needless shortages for NHS staff.
The NHS said it was also offering temporary work to final-year medical students and student nurses, as well as retirees.
And those who join the "NHS Army" will be assessed to see what kind of help they could offer in the service's battle against the crisis.