Mass protests against police brutality that have brought thousands of people out of their homes and onto the streets in cities across America are raising the spectre of new coronavirus outbreaks, prompting political leaders, physicians and public health experts to warn that the crowds could cause a surge in cases.

While many political leaders affirmed the right of protesters to express themselves, they urged the demonstrators to wear face masks and maintain social distancing, both to protect themselves and to prevent further community spread of the virus.

More than 100,000 Americans have already died of Covid-19, the disease caused by the new coronavirus. People of colour have been particularly hard hit, with rates of hospitalisations and deaths among black Americans far exceeding those of whites.

The spontaneous outpouring of protests are occurring as many states have warily begun reopening after weeks of stay-at-home orders with millions of American unemployed. Restaurants, schools, beaches and parks are under scrutiny as the public tentatively practices new forms of social distancing.

In Los Angeles, where demonstrations led to the closing of virus testing sites on Saturday, mayor Eric Garcetti warned that the protests could become “super-spreader events”.