National Bank of Greece dropped 13.5% while Alpha Bank fell 4.3% and Piraeus Bank slipped 2.8%.

WSJ: European Stocks Post Small Losses

Alpha Bank has called an emergency meeting of shareholders for Thursday, with Piraeus Bank arranging its meeting for Friday.

BBC: Greek cash machine

Greece's four biggest lenders were the biggest decliners on the Dow Jones European banking stocks index on Wednesday: National Bank, EFG Eurobank, Alpha Bank and Piraeus Bank.

FORBES: Europe Markets Brief

National Bank of Greece (NBG) and Eurobank fell by 30% in morning trade, while Alpha and Piraeus lost up to 20%.

BBC: Greek cash machine