ATHENS/LONDON (Reuters) - The Greek parliament prepared to adopt a harsh austerity plan in the face of violent unrest, as European Central Bank inaction disappointed markets fearful a debt crisis will engulf the euro zone.

The euro and world stocks fell for a third day yesterday as investors fled risk amid signs that Athens' woes are spreading to other weak euro economies, testing whether European governments are willing to extend a bailout devised for Greece alone.

Policymakers' attempts to talk down the risk of contagion and scare off "speculators" had little impact on traders unimpressed by the slow EU response to the crisis.

"There's no let-up in concerns that the euro zone debt crisis could continue to worsen and as a result equity markets across the globe remain under pressure," said Ben Potter, analyst at IG Markets.

After ECB President Jean-Claude Trichet said a meeting of the bank's governing council had not discussed buying bonds to combat the crisis, yield spreads widened for weaker eurozone countries at risk of being sucked in to the debt crisis.

The remark was taken as "massively negative for the periphery" of highly indebted European states, one trader said.

Trichet said the council had not discussed default procedures. "Greece, of course ... will not default," he said.

"The markets want something more specific. They want money flowing to Greece and something like government bond purchases," said Thomas Meissner of DZ Bank.

Wolfgang Schaeuble, finance minister of Germany which is shouldering the biggest burden in the Greek bailout, said any restructuring of Greek debt would cause "exactly the kind of conflagration that we could no longer control".

"We are in a really fundamental crisis, the stability of the euro is really at stake," he added.

European Council President Herman van Rompuy, who will chair a euro zone summit on the crisis today, was the latest top EU official to try to erect a verbal firewall, saying the situation of Portugal or Spain had nothing to do with Greece.

"What I now see are totally irrational movements on the markets set off by unsubstantiated rumours, for instance yesterday with Spain, but also as regards Portugal," he said.

The cost of insuring Portuguese and Spanish debt as well as Greek debt against default leapt to new peaks before a closely watched auction of 5-year Spanish bonds. Yields jumped for the auction but there was no shortage of demand.

The Greek government vowed not to retreat a single step from unpopular wage and pensions cuts and tax rises despite violence in Athens that claimed three lives on Wednesday when rioters set fire to a bank and fought running battles with police.

"This is the time for change. There is not a single day or hour to lose," Prime Minister George Papandreou told parliament.

"We will press ahead, even if we have to walk alone, without the backing of other parties," Finance Minister George Papaconstantinou said.

The Socialist government has a comfortable majority but the main conservative opposition party has vowed to vote against the austerity bill, dashing hopes of political consensus which analysts said would have improved the chances of implementation.

Greek newspapers condemned the violence but some said it was now up to Greece's leaders to set a course people could follow.

"Whether we self-destruct, whether we go bankrupt, depends now on our leaders, but also on all of us," said centre-right daily Kathimerini.