Thousands of Occupy Wall Street supporters have marched on Wall Street, swelled by the backing of more big US unions and backed by a national student day of action.

Amid fine autumn sunshine and in a festive mood, an estimated 15,000 protesters brought Lower Manhattan to a standstill.

The march passed off largely peacefully. But as darkness fell, there were pockets of ugliness when police tried to prevent protesters from advancing on Wall Street itself. Protesters were funnelled behind tight barricades, leading to a number of clashes and arrests.

A senior New York police officer swings his baton to try and stop protesters from entering Wall Street. Photograph: Craig Ruttle/AP

Still pictures and video footage have emerged, showing a senior police officer beating back protesters with a baton.

Pictures also showed officers using pepper spray on protesters. Officers were attempting to block marchers from pushing down Broadway and into the highly-protected Wall Street, home of the New York Stock Exchange.

Protesters earlier gathered in Zuccotti Park in Lower Manhattan in preparation for the march. Students met in Washington Square, after classes at nearby New York University. Both groups converged on Foley Square, where union members were gathering.

There were predictions that the march could be bigger than Saturday's demonstration, when more than 700 people were arrested after being corralled by police on Brooklyn Bridge.

Occupy Wall Street protesters: legal observers giving rights advice. Photograph: Karen McVeigh

In the pre-march build-up at Zuccotti park, legal observers from the National Lawyers Guild gave the crowd lessons in their rights and handed out leaflets with advice on what to do if stopped by police or arrested. In Foley Square, thousands gathered, and a party atmosphere reigned.

James P Hoffa, leader of the Teamsters Union, which represents 1.4m workers. confirmed its backing for Occupy Wall Street. Here's his statement:

No one should be surprised that Occupy Wall Street is gaining support and spreading quickly around the country. The American Dream has disappeared for students, whose reality is debt and unemployment. The dream disappeared for workers forced to take wage cuts by employers sitting on billions of dollars in profits. The dream disappeared for working families who paid too steep a price for Wall Street's greed, stupidity and fraud. It's clear what this movement is all about. It's about taking America back from the CEOs and billionaires on Wall Street who have destroyed our nation's economy. It's about creating good jobs. It's about corporate America treating its workers and customers with honesty and fairness and paying its fair share to stimulate the economy. Teamsters all over the country are participating in Occupy Wall Street events, and I support and encourage them. We stand in solidarity with Americans who want better lives for themselves and for future generations.

In an earlier visit to Florida, Mitt Romney, the Republican presidential hopeful, prompted anger by suggesting the Occupy Wall Street protesters represented "class warfare".

Another candidate, Herman Cain, also addressed the Occupy Wall Street protests. He said in a Wall Street Journal interview: