China on Monday urged the United States to safeguard the legal rights of ethnic minorities, with protests escalating nationwide in the wake of the alleged killing of a black man by a white police officer last week in Minneapolis.

"The racial discrimination suffered by minorities in the United States is a chronic illness" in the country, Chinese Foreign Ministry spokesman Zhao Lijian told reporters, calling on Washington to urgently solve such a problem.

Protestors march during a demonstration organized by Black Lives Matter following the death of George Floyd on May 30, 2020 in Los Angeles, California. (Getty/Kyodo)

At least 40 cities have imposed curfews, including the U.S. capital, and state military forces have been activated in many places to quell the protests, many of which have turned violent with people looting and setting fire to buildings and vehicles, U.S. media said.

It was the first time since 1968, the year when civil rights activist Martin Luther King Jr. was assassinated, that so many local leaders have issued curfews in the face of civil unrest, according to The New York Times.

"Why has the United States accused the Hong Kong police (of using force)...but has threatened to shoot its domestic protesters and has even called in National Guard troops?" Zhao said. "The U.S. approach is the most typical double standard in the world."

Protests have erupted across the United States, and demonstrations have also spread to some European countries after George Floyd, 46, was allegedly killed by a police officer following his arrest outside a shop in the Midwestern state of Minnesota.

In Washington, near the White House, police on Sunday countered protesters by firing tear gas.

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