Demonstrators in London protesting against the G20 summit smashed windows and briefly entered the Royal Bank of Scotland Wednesday, before riot police with truncheons and shields pushed them back. 

Protesters also tried to storm the Bank of England, whose windows were covered with plywood in anticipation of violence.

The clashes broke out as world leaders prepared to open their crisis talks on the global economic downturn.  Thousands of demonstrators filled the narrow streets of the City of London, the banking and financial center of the British capital, for what organizers called "Financial Fools Day" protests. 

Police also blocked crowds from marching on the London Stock Exchange and other financial institutions.  Reporter Tom Rivers told VOA the protesters appeared to be a mix of anarchists, anti-capitalists and environmentalists.

The Times newspaper described the British capital as "Fortress London."

Some of the demonstrators came away bleeding from their clashes with the police, who wore bright yellow jackets to identify themselves in the crowds.  Authorities say about 2,500 uniformed officers are assigned to security duty for the G-20 summit, with many more deployed to protect the world leaders and international officials attending the meetings.