The biggest U.S. banks are banding together to rescue beleaguered San Francisco lender First Republic (FRC) with $30 billion of uninsured deposits, an unusual joint effort to stabilize a rival and restore calm following a volatile week.

The infusion from 11 of the nation's biggest banks, including JPMorgan Chase (JPM) and Bank of America (BAC), follows a steep drop in the shares of First Republic, which was the nation's 14th-largest bank as of Dec. 31 with $212 billion in assets.

JPMorgan, Bank of America, Citigroup (C) and Wells Fargo (WFC)—the four largest lenders in the U.S. by assets—deposited $5 billion apiece. Goldman Sachs (GS), Morgan Stanley (MS) each deposited $2.5 billion while U.S. Bancorp (USB), Truist (TFC), PNC (PNC), State Street (STT) and Bank of New York Mellon (BK) each deposited $1 billion. The deposits have to stay at First Republic for 120 days and earn interest at the same rate of current depositors, according to a person familiar with the pact.

"The actions of America’s largest banks reflect their confidence in the country’s banking system," the banks said in a joint release. "Together, we are deploying our financial strength and liquidity into the larger system, where it is needed the most." Federal Reserve Chair Jerome Powell, Treasury Secretary Janet Yellen and two other regulators said in a joint statement that "this show of support by a group of large banks is most welcome, and demonstrates the resilience of the banking system."

The extraordinary infusion from First Republic's competitors is an attempt to stop a slide for the California lender that began during last week's failure of another lender in the same state: Santa Clara-based Silicon Valley Bank. An initial infusion of $70 billion in financing from JPMorgan and the Federal Reserve announced Sunday failed to alleviate the pressure.

First Republic's shares plummeted again this week after S&P Global and Fitch Ratings downgraded the bank's credit rating. Shares recovered Thursday after The Wall Street Journal and Bloomberg reported details of the industry pact, with the stock up 10% at the close. CNBC also earlier reported the 120-day term of the deposits provided by the 11 banks.