Bond dealers also indicated Greek 2-year yields at 48 percent, a surge of 13 percentage points, but no trading took place as the Greek markets regulator requested their suspension last week following the country's default on an IMF loan.
National Bank of Greece's US-listed shares were down 15 per cent in pre-market trading, while the Global X FTSE Greece ETF (exchange-traded fund) was down 11.2 per cent.
The Greek stock market has been shut since last week but US-listed assets are still being traded.
Top euro zone shares were down 1.6 per cent.
"So far the stock-market reaction has been negative but not disastrous," said Laith Khalaf, senior analyst at Hargreaves Lansdown.
"This suggests a fair degree of pessimism over the Greek referendum result had already been priced into markets.
"After all, this bolt has hardly come out of the blue."
Image: 'No' supporters celebrate their victory in the referendum by the parliament in Athens, Greece July 5, 2015. Photograph: Dimitris Michalakis/Reuters
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