Officials said 90 people were arrested Wednesday during protests marking the summit of world political and financial leaders, The Times of London reported.
Demonstrators were expected to protest at the London Stock Exchange, as well as the heavily guarded Excel Center, site of the summit.
Officials said protesters threw bottles at emergency medical personnel as they tried to resuscitate a man who collapsed near the Bank of England during the protests. The man eventually was pronounced dead at a hospital.
Police chiefs reported officers faced "high levels of violence" in isolated incidents throughout the day, The Times said.
A group of protesters trashed equipment, tagged walls and threw a chair through a window after more than 4,000 mostly peaceful demonstrators gathered near the Bank of England, The Times said.
While the majority of participants were peaceful, Cmdr. Simon O'Brien of the Metropolitan Police said police would track down the people believed responsible for the violent outbreaks. O'Brien said some of the potential ringleaders were followed by helicopter as they left.
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