A strong sense of pessimism shrouded the start of an economic summit of rich and emerging economies Thursday, with President Barack Obama and fellow world leaders arriving in Seoul sharply divided over currency and trade policies.

The Group of 20 summit, held for the first time in Asia, has become the centerpiece of international efforts to revive the global economy and prevent future financial meltdowns.

Failure in Seoul could have severe consequences. The risk is that countries would try to keep their currencies artificially low to give their exporters a competitive edge in global markets. That could lead to a destructive trade war. Countries might throw up barriers to imports — a repeat of policies that worsened the Great Depression.

Hopes had been high that the Group of 20 — encompassing rich nations such as Germany and the U.S. as well as growing giants such as China and Brazil — could be the world forum for hashing out an economic way forward from financial crisis.

But agreement appeared elusive as the summit began, divided between those such as United States that want to get China to allow its currency rise and those irate over U.S. Federal Reserve plans to pump $600 billion of new money into the sluggish American economy, effectively devaluing the dollar.