London's financial district is left facing a major clear-up operation after the day of protest that turned violent.

Sixteen people were arrested after buildings were damaged, and one woman is still in hospital.

The BBC's Alva McNicol: "Many were hailing the demonstrations as a success"

Clashes between police and protesters flared up in the financial heart of London on Friday during a 'Carnival against Capitalism' to mark the opening of the G8 world economic summit in Cologne - and continued into the early hours of Saturday.

Offices, hospitals and restuarants in the Square Mile were damaged by some of the thousands of people who converged on the City of London, targeting banks and the London International Financial Futures Exchange.

Sixteen people were arrested as protesters rampaged through the area, attacking police and buildings with bricks, breeze blocks and scaffolding poles.

At least 42 demonstrators and four police officers were injured, including two protesters who were knocked down by a police van.

Thousands crammed into the Square Mile to take part in the demonstration

A City of London spokesman said on Friday: "Missiles are being thrown at police and police vehicles have been damaged. Officers are keeping the crowds under surveillance.

"They are throwing stuff from building sites - bricks, concrete blocks and other debris," he added.

At least 200 demonstrators continued their protest through the early hours of Saturday at Trafalgar Square.

Before midnight, trouble flared up again and police were pelted with bottles when they tried to arrest one of the protesters.

Chief Inspector Ed Bateman said gas had been used against some of his officers.

He said: "They've been through something horrific. I certainly haven't seen gas used before. I think it was possibly mustard gas or a form of gas that got into my officers' eyes.

"They couldn't work, and when that happened people would throw things at them. It was pretty dreadful conditions, and they did a very good job."

But the Lord Mayor of London, Lord Levene, criticised police tactics for being over-zealous.

Run over by police van

A female protester was knocked down by a reversing police van on London Wall.

The woman, in her mid-20s, was taken to the Royal London Hospital suffering from concussion and a fractured leg. She was said to be in a "satisfactory" condition on Saturday.

A police spokesman confirmed: "The police van was surrounded by demonstrators on London Wall and was under heavy attack and was trying to extricate itself from that when this woman was knocked down," he said.

"We very much regret the fact that this person has been injured but we have made every effort throughout the day, and prior to today in our planning, to minimise the risk of injury to any person."

A second person was knocked down by a Metropolitan Police van which had been called in to assist the City force. The victim was also taken to the Royal London Hospital for treatment but later discharged.

Traffic brought to a standstill

Some 50 protesters smashed the glass doors of the London International Financial Futures Exchange (LIFFE).

They eventually left under police escort and were shepherded into a nearby square where renewed clashes broke out.

Some protesters managed to get their message across peacefully

LIFFE traders went onto their fire escape and threw trading cards onto the protesters in an act of defiance. Trading was halted as the building was evacuated.

Earlier around 300 cyclists had disrupted traffic in London's financial heartland.

Carrying banners with slogans like "Money Kills", they rode slowly into the city centre and brought traffic around the Bank of England in Threadneedle Street to a standstill.

Eight demonstrators managed to enter Lloyds Bank in Cheapside and some chained themselves inside.

A further six went into the NatWest bank on the same street but left after police were called.

Two other activists were removed from Tower Bridge after they tried to climb the structure. Campaigners also daubed pink paint on the door of the London Metal Exchange.

Initially there were less than 500 campaigners in the City, but crowds then began to gather around Liverpool Street station before the violence flared.

Concern for City workers

A City police spokesman added: "Our paramount consideration will be to prevent City workers from being the victim of offences."

Anne Philpott, who works in an insurance company, said: "I'm not sure the protesters will achieve much this way. There is more chance of irritating people."

A retired City worker was more direct and disparaging. "They all live in trees and swamps," he said.

But many protesters were anxious to promote a peaceful message.

Des Kay, of the Save the World Club, said: "As Gandhi said `There's enough on this planet for everyone's needs but not for everyone's greed'. That is what today is all about."

The London rally had been timed to coincide with other rallies around the world marking the start of the Group of Eight rich countries' summit.

German police were expecting up to 100,000 demonstrators to protest in Cologne calling for the burden of debt in the world's poorest countries to be cancelled.

As the protests continued, world leaders announced they had reached to a deal to forgive up to $90bn or 40% of that debt.