Investors were already anxious about the collapse of Silicon Valley Bank and Signature Bank, two midsized US financial institutions. Now, they are fretting over uncertainty at a bank with links to others around the world. Their concerns about Credit Suisse have them questioning the stability of the global financial system.

Credit Suisse officials have a history of troubles, from trading losses to repeated shakeups among executives. They have now identified what they call "material weaknesses" in oversight of their financial reporting.

The Saudi National Bank agreed last year to invest 1.6 billion dollars to help turn Credit Suisse around. Its 10-percent stake made it the bank's largest shareholder.

However, on Wednesday the Saudi Bank ruled out raising that stake, which would have subject it to additional Swiss regulations.

Investors immediately tried to unload Credit Suisse stock. At one point, shares were down 30 percent and reached a record low.

The contagion also spread through global markets. The Dow Jones Industrial Average, at one point, plunged more than 700 points.

Swiss policymakers said in a statement that the central bank will step in and provide Credit Suisse with a backstop "if necessary."