British authorities arrested 76 people at a mass "die-in" in London held in solidarity with demonstrations sweeping the United States over recent controversial killings of black men by police.

Hundreds of demonstrators blocked the Westfield shopping mall in west London by lying down on the floor, many holding placards echoing the "Black lives matter" and "Hands up" slogans branded on signs at the US protests.

Rallies have been held across the US in recent months after authorities decided not to press charges in two separate incidents in which white police officers killed black men.

The decisions have special resonance in the British capital, where the police shooting of 29-year-old black resident Mark Duggan was a factor in the outbreak of riots in 2011.

One protest banner at the mall read "Solidarity with Ferguson", in reference to the Missouri suburb which saw riots over the shooting of unarmed 18-year-old Michael Brown by a white officer.

Protesters also chanted "We can't breathe", in reference to the last words gasped repeatedly by 43-year-old Eric Garner, a father of six killed in a police chokehold in New York in July.

British police said that during the demonstration a group of protesters outside the mall tried to force their way in, "assaulting security staff and causing damage to property".

In response, police cordoned a large crowd of people outside the mall and arrested 76 on suspicion of public order offences. One man was also arrested on further suspicion of assault.

Those arrested were taken away in red double decker buses.

"We will always work with those that wish to demonstrate lawfully, as the majority of protestors did," said chief superintendent Mark Bird.

"However, we will not tolerate the small minority that offer violence or commit other criminal acts, such as that witnessed outside Westfield."

The arrests were criticised by protesters as an intimidation tactic aimed to dissuade demonstrations.

It was the second large London protest in a fortnight over the issue.

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