United Nations General Assembly has opened its annual general debate, with global financial crises dominating the agenda.

In his speech kicking off the debate on Tuesday, UN Secretary General Ban Ki-moon called for "strong global leadership".

"In this new world our challenges are increasingly those of collaboration rather than confrontation. Nations can no longer protect their interest or advance the well being of their people without the partnership of the rest."

He also called for UN reform and said the current system of contracts and conditions of service is "dysfunctional" and "demoralizing."

United States President George W Bush gave his final UN General Assembly speech, assuring worried world leaders that his administration will work quickly with Congress to address the U.S. financial crisis.

"I know that many of you here are watching how the United States government will address the problems in our financial system. In recent weeks we have taken bold steps to prevent a severe disruption of the American economy, which would have a devastating effect on other economies around the world."

French President Nicolas Sarkozy also called on world leaders to meet at the end of the year to study the lessons of financial crises that the world has experienced.

Nearly 120 heads of state or government were in attendance for Tuesday's opening of the general debate of the General Assembly, and representatives of all 192 member states are expected to take the podium before it concludes next week.