Shares on the Athens Stock Exchange tumbled after it reopened following a five-week shutdown. The index was 23 per cent down in early trading before recovering a little to be 16 per cent down in mid-afternoon trading. Greek banks are not doing any better. National Bank of Greece, a benchmark stock, was down 30 per cent a few minutes after the opening. The banking index covering the largest Greek banks also hit the volatility limit, as new evidence emerged on the damage to Greece's economy from the country's debt crisis.