New York has gone into security lockdown as it prepares for the United Nations summit, the biggest meeting of world leaders in history.

Police set up metal fences around the headquarters of a major bank in New Jersey, blocked off two streets, and armed themselves with assault rifles after authorities warned of a terrorist attack on financial institutions.

Former New York Mayor Rudolph Giuliani, the man who helped America through the September 11 attacks, landed in London tonight, hours before being made an honorary knight.