It is not known whether Banksy, whose identity is a closely guarded secret, or somebody else attached the fabric face mask to the painted girl.
The newly adorned mural did not appear on Banksy’s Instagram page where he usually posts images of his work.
The COVID-19 pandemic has already inspired the artist.
He unveiled a scene of his trademark stencilled rats running amok in a bathroom rather than on the streets last week, reflecting official advice form the British government to stay at home.
“My wife hates it when I work from home,” he commented alongside the photos.