Banks lead global turmoil in stocks as ‘Brexit’ vote sparks panic

Banks hit hard by Brexit
Investors seek safety plays as pound sinks
What next for Britain?

Bank stocks plummeted to the bottom of indexes across Europe Friday after the U.K. voted to quit the European Union (EU) and stunned global markets.

The U.K. people voted by 51.9 percent to 48.1 percent to quit the 28-country union, shocking markets that had priced in a win for "remain."

Shares of U.K. banking giants RBS, Barclays and Lloyds Banking Group all closed more than 17 percent lower, sharply underperforming the FTSE 100 index.

These banks retain a focus on the U.K. — unlike rival HSBC, which also has a strong Asia base. Shares of HSBC closed around 1.4 percent down on Friday.

Each of RBS, Barclays and Lloyds issued statements aimed at reassuring investors, customers and staff on Friday.

"The strategy we announced on March 1, 2016 was not conditional on the UK remaining in the EU. We are a transatlantic consumer, corporate and investment bank, anchored in the U.K. and the U.S.," Barclays chief executive, Jes Staley, said in a statement emailed to CNBC.

RBS said there would be no immediate impact on their services, but that time would be required for the bank to "work through the implications of the vote with regulators."

Bank of England Governor Mark Carney announced on Friday that the central bank would act to support U.K. financials and the broader economy as required.

"As a backstop, and to support the functioning of markets, the Bank of England stands ready to provide more than £250 billion ($343 billion) of additional funds through its normal facilities," he said in a public statement.

S&P Global Ratings said the "leave" vote would have no immediate impact on U.K. commercial banks' ratings.

"We see the effects of a leave vote on these banks as indirect, arising from potential adverse consequences for economic activity, new business volumes, asset prices, and demand for U.K.-related debt ... volatility may interrupt wholesale debt issuance and affect the values of financial assets in the near term," the ratings agency said in a report on Friday.

European banks react

European banks headquartered outside of the U.K. also fell sharply on Friday. Shares of Greek and Italian banks, which were already under pressure because of concerns about their bad debt piles, were notably poor performers.

Shares of Greece's Alpha Bank and Eurobank Ergasias both closed around 30 percent lower, while Italy's Intesa Sanpaolo declined by around 23 percent.

Shares of French and German banks also tumbled, with Deutsche Bank tending around 14 percent lower on Friday.

"I'm afraid that this is not such a good day for Europe," Deutsche Co-CEO John Cryan said in a statement on the bank's website on Friday.

"At this stage, we cannot fully foresee the consequences, but there's no doubt that they will be negative on all sides. As a bank headquartered in Germany and with a strong presence in the U.K., we are well prepared. However, there's no doubt that the uncertainty created by the referendum's results will be a challenge," he added.

Timeline: UK votes to leave EU

Shares of U.S. banks also fell, with JPMorgan Chase down more than 5 percent around the close of European markets.

Early on Friday, JPMorgan's top executives said they might seek to change the bank's legal structure and geographic positioning in response to the upcoming "Brexit."

The bank currently employs 16,000 people in the U.K, predominately in London.

"Regardless of today's outcome, we will maintain a large presence in London, Bournemouth and Scotland, serving local clients as we have for more than 150 years… In the months ahead, however, we may need to make changes to our European legal entity structure and the location of some roles. While these changes are not certain, we have to be prepared to comply with new laws as we serve our clients around the world," JPMorgan Chase CEO Jamie Dimon, JPMorgan Asset Management CEO Mary Erdoes and Daniel Pinto, chief executive for corporate and investment, said in the statement.

Follow CNBC International on Twitter and Facebook.