US Federal Reserve chair Janet Yellen said it is appropriate for US central bankers to “proceed cautiously” in raising interest rates because the global economy presents heightened risks.

Despair over the economy sent Wall Street plunging again today, propelling the Dow Jones industrials down 733 points, or 7.8%, to their second-largest point loss ever.

The Dow Jones industrial average climbed 147.21, or 1.8%, to close at 8,512.01.