MADRID - Chanting for justice, protesters rallied in European cities on Sunday, joining a wave of demonstrations sparked by the death of African American George Floyd at the hands of US police.

A video of the incident with Floyd pleading for his life in Minneapolis as a white police officer knelt on his neck has prompted angry rallies worldwide, even as countries continue to discourage large gatherings to curb the coronavirus pandemic.

Several thousand people massed Sunday outside the US embassy in Madrid, shouting  "I cannot breathe", Floyd's last words, and demanding racial justice.

"Racism knows no borders," said Leinisa Seemdo, a 26-year-old Spanish translator from Cape Verde. "In all the countries where I have lived, I have experienced discrimination because of the colour of my skin."

At a police cordon, they knelt in silence in a gesture against racism first made by US football player Colin Kaepernick in 2016.

Rome's Piazza del Popolo ("People's Plaza") also fell silent for eight minutes -- around the time Floyd was pinned down by the white policeman -- with thousands of people taking a knee in memory of Floyd, their fists in the air.

"We can't breathe," shouted the crowd, after the collective silence.

"It's really hard to live here," said Senegalese migrant Morikeba Samate, 32, one of the thousands to have arrived in Italy after risking the perilous crossing across the Mediterranean.

Opposition to that wave of migration buoyed the far-right in Italy and elsewhere in Europe, creating a culture of mistrust those in the crowd said needed to end.Floyd's death last month has unleashed the most serious civil unrest in America since Martin Luther King was assassinated in 1968.

Tens of thousands of protesters have rallied this week across the country from New York and Washington to San Francisco.

The police officer, Derek Chauvin, has been charged with second-degree murder while three fellow officers face lesser charges.