European banks took a beating in early trading Friday, with Barclays PLC down nearly 30% at one point and other investment banks also suffering from widespread market uncertainty after the U.K. voted to leave the European Union.

Shares of Switzerland's Credit Suisse Group AG were trading down 13%, and Standard Chartered PLC was down around 8%. Shares in Germany's biggest bank, Deutsche Bank AG, were down 17% just before Prime Minister David Cameron began his address Friday morning in which he said he would step down.

Shares of HSBC PLC, which is seen as less exposed to the EU exit due to its significant Asian operations, fell by 4.8%.

Spain's Banco Santander SA, which has significant exposure to the U.K. through its Santander U.K. unit, was also pummeled, with its share price down 20.8%.

Things looked even worse for Italian banks Friday morning. The majority of Italian shares failed to start trading at market opening in Milan, as trades didn't go through because investors were dumping Italian shares at prices not matching the ones offered by buyers.

Theoretically based on orders placed in the market, UniCredit SpA shares were down 36%, Intesa Sanpaolo SpA's were down 23%, and Mediobanca's were down 50%. A strategist said that at this level of discrepancy between bid and ask prices the stocks wouldn't manage to start trading.

"Financial sectors were really expecting a 'remain,'" said Joseph Dickerson, an equities analyst with Jefferies International. "We are now entering a long period of uncertainty."

Write to Sara Schaefer Muñ oz at Sara.Munoz@wsj.com, Jenny Strasburg at jenny.strasburg@wsj.com and Giovanni Legorano at giovanni.legorano@wsj.com

(END) Dow Jones Newswires

June 24, 2016 05:05 ET (09:05 GMT)