They were warned by Prime Minister Scott Morrison of Australia against attending Black Lives Matter marches on Saturday because of the coronavirus risk, but tens of thousands would not be deterred.

The health minister in Britain pleaded with residents not to gather for similar demonstrations in cities like London, Manchester and Birmingham to stop the virus’s spread. But throngs showed up anyway — despite the cold weather, the spitting rain and warnings by the police that mass gatherings would violate the rule that only six people from different households could gather outside during the pandemic.

From Paris to Berlin — as in demonstrations this past week in Japan, Sweden and Zimbabwe — people around the world once again turned out in solidarity with Americans protesters calling for justice in the death of an African-American man, George Floyd, at the hands of the police in Minneapolis.

They showed up in circumstances that made it almost impossible to adhere to social distancing regulations. Tens of thousands flowed to Parliament Square in London on Saturday afternoon, shouting anti-racist slogans and carrying signs paying homage to Mr. Floyd, 46, who died after a white police officer held his knee to Mr. Floyd’s neck in Minneapolis on May 25.

Though most people were wearing masks, their collective chants could be heard loud and clear: “George Floyd,” “Black lives matter,” “No justice, no peace,” they said. Footage showed hundreds streaming toward the U.S. Embassy on foot and by car, hooting and honking horns.

Silence fell among the crowds for about minute when the protesters all knelt on the wet ground, and many raised their fists in the air.

The world has been transfixed by the unrest in the United States amid video footage of brutal clashes between police and protesters, along with episodes of looting and destruction — though many cities held peaceful marches and vigils in Mr. Floyd’s memory. The global demonstrations, continuing for a week now, were inspired by the demonstrations in the United States to call for an end to racism and police brutality in their own countries.

On Tuesday, almost three dozen Kenyan and Americans gathered outside the U.S. Embassy in Nairobi in support of demonstrations in the United States. The protesters wore masks, chanted slogans like “Down with police brutality” and carried posters that read, “Silence is violence.”