NEW YORK/LONDON - Credit Suisse shares shot up by more than 30 per cent as trading opened in Zurich on Thursday after turning to the central bank in a bid to temper fears over its finances.

It was announced last night that the lender would borrow up to 50 billion Swiss francs (£44 billion) from the Swiss National Bank to strengthen its liquidity.

The troubled banking giant said it was taking decisive action to shore up its finances after its shares nosedived 30 per cent on Wednesday.

Fear about the unseen risks to the financial system rippled across the globe on Wednesday, breaking the brief calm that had settled over markets and deepening worries that a banking crisis could threaten the economy.

The turmoil was set off by a panic over the health of Credit Suisse, the 166-year-old Swiss bank that has been reeling from years of mismanagement and poor risk control and that warned this week about problems in its accounting practices.

Though the Swiss bank’s difficulties differ from the woes of the American banks that have collapsed in recent days, concern about Credit Suisse added to a sense of dread about the economy in general. In an attempt to calm investors’ nerves, Switzerland’s central bank, the Swiss National Bank, said late in the day that it would step in if necessary to keep Credit Suisse afloat.

This year was already going to be an unpredictable one for the economy and the markets, coming after a tumultuous 2022, but “that uncertainty has only gone higher,” said Dan Ivascyn, the chief investment officer of Pimco, the bond-fund manager with roughly $2 trillion in assets.

Wall Street has been on edge ever since the collapse of Silicon Valley Bank and Signature Bank, which were seized by regulators after suffering devastating runs on deposits. Policymakers have sought to contain the risks by backstopping lenders, and although those efforts have helped ease concerns, Wednesday’s trading showed that the anxiety isn’t fully resolved.

Credit Suisse’s shares plunged to a new low after the bank’s largest shareholder, Saudi National Bank, ruled out providing it with more money as it struggles with its latest turnaround plan. The Swiss National Bank said it stood ready to support Credit Suisse if necessary, but not before shares across Europe were also hard hit, with stocks of many of the region’s biggest banks falling sharply.

Rating agencies have noted that the European banks have less exposure to the same risks that took down small lenders in the United States, while investors took some comfort from the swift action taken by the authorities around the world.

Shortly before the markets opened in the United States, S&P Global Ratings cut the credit rating of First Republic Bank, another American lender that investors are worried about, into so-called junk territory. The agency said that the risk of deposit withdrawals was “elevated,” noting that the bank’s $176 billion deposit base is more concentrated than many other banks, with a large share commercial clients holding balances above the $250,000 limit insured by the government.

First Republic skidded 21 percent on Wednesday and PacWest Bancorp, another bank whose shares have recently come under pressure, fell 13 percent, with the volatility triggering temporary halts in trading at various points during the day.

Central bankers in the eurozone meet on Thursday to decide whether or not to keep raising interest rates in light of the ensuing turmoil, and until recently had been expected to keep aggressively pushing rates higher. That meeting will be followed by the Federal Reserve’s, which will happen next week.