Carrying 503 of 596 possible votes, Merkel can be confident she has a strong mandate from German lawmakers.
All the parliamentary groups in the Bundestag – with the exception of the socialist Left party – had earlier signed a text giving Merkel their blessing to increase the firepower of the European Financial Stability Facility(EFSF) without EU paymaster Germany putting in more money.
At the Brussels summit later on Wednesday, the heads of the 17 eurozone countries will hold talks in a bid to thrash out a solution to what is seen as the worst economic emergency in the EU's history and a situation threatening to tip the world into recession.
Earlier in the day Merkel had said that the crisis must be resolved "now or ... never."
"The fundamental weaknesses and holes in the construction of the economic
and monetary union must either be addressed now or, I say, never," she told
German parliamentarians. "And if we address them now, then we will have seized the opportunity this crisis presents us. Otherwise we will have failed," she said.
Merkel told the Bundestag, the lower house of the German parliament, that resolving the weaknesses of the common currency could only be done with changes to European treaties.
"Where does it state that treaty changes must take a decade?" she said, adding that treaty changes always carry risks because they must approved by all 27 members of the European Union.
The brief text, obtained by news agency AFP, refers to two models being examined for bolstering the bailout fund.
One would insure jittery investors against potential future losses from the debt of shaky countries, hopefully encouraging them to continue to buy bonds from the likes of Italy, Portugal and Spain.
The second calls for aid to be co-financed by public or private investors, including foreign countries. "The two models are not mutually exclusive," the text says.
Earlier on Wednesday, the China Daily newspaper reported that Beijing and other emerging powers had agreed to help the eurozone, citing a source close to EU decision makers.
"It is going to be a long day," said Merkel's spokesman Steffen Seibert, on
microblogging website Twitter.