Piraeus Bank, Eurobank and Alpha Bank sank almost 30 percent as of 12:30 GMT, while the National Bank of Greece plunged 25.62 percent.
The four banks – National Bank of Greece, Piraeus Bank, Alpha Bank, and Eurobank – account for 91 percent of Greek banking assets.
Athens Stock Exchange General Index (ASE) was losing 4.33 percent, after closing at its lowest level since September 2012 on Tuesday. Monday’s plunge was the worst in 30 years for the ASE.
The Greek banks’ index is showing its most parlous result since 1995. Greek stocks have lost more than 88 percent of their value since 2007.