Several thousand demonstrators have marched across New York's Brooklyn Bridge on a day of protest that saw solidarity rallies across the US, BBC reports.

At least 300 people were arrested just in New York, many of them as trouble flared near the stock exchange.

Occupy Wall Street activists started the day by marching through the city's financial district and later rallied at subway stations during rush hour.

Mayor Michael Bloomberg said five police officers had been injured.

Thursday's nationwide protests were seen as a test of Occupy Wall Street's momentum, as the grassroots movement against economic inequality marked two months since it began.

It was planned before demonstrators were swept two days ago from New York's Zuccotti Park, where they had camped since mid-September.

As darkness fell on Thursday evening, protesters - their numbers swelled by union activists - moved on to the Brooklyn Bridge.

Police arrested 65 of them who walked on to the bridge roadway, but otherwise let them pass.

Demonstrators massed earlier nearby in lower Manhattan's Foley Square, where their chants boomed off the surrounding government buildings.

Police tried to pen the protesters using barricades, but without success.

"This is a critical moment," demonstrator Paul Knick, a software engineer, told AP news agency.

"It seems like there's a concerted effort to stop the movement, and I'm here to make sure that doesn't happen."