Protesters clashed with police, who fired tear gas early Wednesday, several hours before the Greek parliament was to vote on an austerity package.
The vote on a 28.4 billion-euro ($40.8 billion) package of taxes, spending cuts and sell-offs is crucial for Greece to secure international aid to stave off bankruptcy, which is threatening the stability of the eurozone.
Police drove back a group of 400 leftwing demonstrators in front of the Hilton hotel in central Athens, who were making their way towards Syntagma square, where parliament is located, and dispersed them with tear gas.
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Angry workers on Tuesday launched a 48-hour general strike, which brought about blanket power cuts and ground transport in the capital to a halt.
Lawmakers were due to begin voting on Wednesday afternoon on the austerity measures that would unblock 12 billion euros of emergency loans from last year's 110-billion bailout.
That would then free eurozone finance ministers to start drawing up a second bailout in talks in Brussels on Sunday.
On Tuesday, police fired tear gas on violent protestors on the first day of a 48-hour general strike against the belt-tightening package.
Police said 21 officers were hurt but made only about a dozen arrests despite firebombs setting property ablaze and demonstrators smashing up the marble steps of a luxury hotel facing the legislature to use as missiles.
At least one of Papandreou's own lawmakers has threatened to vote against the whip by way of opposition to this decision.
While Tuesday's protests drew nearly 10,000 onto the parliament's Syntagma Square home, the numbers were fewer than on previous occasions where ritual firebombing unleashed tear-gassing by security forces by way of reply.
A 4,000-strong police contingent will again barricade a wide perimeter running right round the parliament, but self-styled Indignants who have set up camp on the square for nearly seven weeks now have vowed to go head-to-head with this ring of steel in the morning.

