The two mainstream parties that approved the second international £110 billion rescue loan and its stringent requirements for cuts were heavily punished as support surged for the Left and Right.
The shattering of the political status quo threw into doubt Greece’s commitment to meeting the terms of its debt and could spread instability throughout the euro zone.
Weeks of uncertainty are likely to follow as numerous parties vie to cobble a majority coalition, with a fresh election within two months a distinct possibility.
There will also be fears that ensuing political instability will see a return to the street violence that has scarred Athens since the debt crisis surfaced two years ago.
Exit polls said the conservative monolith New Democracy would finish first with a maximum of 20 per cent, while Pasok, the main socialist party, would suffer a dramatic fall to 13-14 percent, a third of what it received when winning the 2009 election. Voters held both responsible for years of mismanagement and corruption.