The announcement, made late Wednesday, has sent a shockwave through the world's markets and has left many analysts believing that the euro zone's central bank is playing hardball at a crucial time for not just Greece, but for the euro zone as a whole.
In Europe on Thursday, banking stocks across the region were down 1.3 percent in the morning session, weighing heavily on wider benchmarks. The sector recovered some ground to close down 0.5 percent on the day.
Greek stocks were down around 5 percent in afternoon trading, before closing over 3 percent lower. Greece's Bank of Piraeus lost 27 percent at the open, the National Bank of Greece was down 26 percent and Alpha Bank lost 13 percent
The rout in Europe's markets comes after U.S. stocks closed mostly lower Wednesday on the news, and dented global sentiment.
CNBC takes a look at why the ECB acted as it did and what it means for Greece and Europe.