A handout picture received from University Hospital Southampton on May 7, 2020 shows an artwork by street artist Banksy called Game Changer on a wall at the University Hospital Southampton, southern England, as a tribute to staff from the National Health Service who are continuing to work during the COVID-19 pandemic. (STUART MARTIN / AFP / UNIVERSITY HOSPITAL SOUTHAMPTON)

A painting by the still-unidentified British street artist Banksy is set to raise more than 3 million pounds (US$4.1 million) for the National Health Service (NHS) when it goes to auction later this month.

The artwork, titled Game Changer, first appeared in Southampton General Hospital on May 6, 2020, during the first wave of the global COVID-19 pandemic.

The painting shows a young boy playing with superhero dolls. While Batman and Spider-Man lie discarded in a bin, the child clutches a masked nurse dressed in the uniform of the International Red Cross flying to the rescue, her cape fluttering and arm outstretched toward the sky.

Auction house Christie's said the painting "offers an image of hope "and "represents a personal tribute to those who continue to turn the tide of the pandemic"

The artist is now auctioning the original canvas with proceeds benefitting the NHS.

A reproduction of the work will remain on view in the hospital.

Auction house Christie's said the painting "offers an image of hope "and "represents a personal tribute to those who continue to turn the tide of the pandemic".

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When the picture was first unveiled, an accompanying note said: "Thanks for all you're doing. I hope this brightens the place up a bit, even if it's only black and white."

The auction house said until now, the work has only been seen in person by frontline medical staff and those admitted to hospital for treatment. The auction marks Game Changer's first appearance outside the hospital.

The painting has a pre-sale estimate of 2.5 million to 3.5 million pounds.

Katharine Arnold, co-head of Post-War and Contemporary Art, Europe at Christie's, said Game Changer is a universal tribute to those around the world fighting on the frontline of the crisis.

"At a time when we can dare to hope once more, and look at life beyond the pandemic, it is important to reflect on the many symbols of strength and hope we have seen internationally since the beginning of 2020," Arnold said. "Banksy's Game Changer was a beacon of light for the staff and patients at Southampton General Hospital and it was the artist's wish to then auction it with proceeds benefitting the NHS. The work pays tribute to the strength and resilience of those who have demonstrated true leadership throughout the pandemic, the staff of our vital NHS, the nation's true heroes."

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The work can be seen from the Duke Street Gallery window at Christie's Headquarters in London until March 15, ahead of the auction on March 23.