Greek legislators were debating throughout Thursday the country's third bailout deal in five years which will unlock further vital international funds to avert a catastrophic default and Grexit.

Ahead of the vote in the plenary scheduled around midnight anti-austerity protesters hit the streets of Athens and ruling Radical Left SYRIZA party "rebels" stepped up pressure on the government to "take an alternative course," as banners waved in front of the parliament read.

With the backing of pro-euro opposition parties, the draft bill containing the 85 billion euro worth deal agreed on Tuesday was expected to easily pass the assembly.

Otherwise, Finance Minister Euclid Tsakalotos warned while addressing the parliament he will have to accept a bridging loan during Friday's Eurogroup so that Athens can repay a billion euro debt to the European Central Bank on Aug. 20.

However, the harsh terms of more spending cuts, tax hikes and reforms in return of more aid over the next three years have been met with strong reactions by citizens in the streets and dissidents within the party of Prime Minister Alexis Tsipras.

The Leftist leader was elected in power in January on an anti-austerity agenda, but now defends the new agreement with lenders as the only way to avert financial meltdown and the worst for Greece.

"Enough is enough. We say no to more austerity," chanted demonstrators who participated in two symbolic rallies called by the umbrella union of civil servants ADEDY and the Communist party KKE on Thursday evening.

Meanwhile, former Finance Minister Yanis Varoufakis dismissed the bailout deal as "unviable" and a dozen SYRIZA lawmakers led by former Energy Minister Panagiotis Lafazanis who have openly suggested return to drachma lately, announced that in coming days and weeks they will form a new "anti-bailout political and social movement."

"The struggle against the new memorandum starts now," read a joint statement which verified media scenarios that a party split was imminent.

Amidst concern of a subsequent government collapse and snap general elections soon, State Minister Alekos Flambouraris told local SKAI television channel on Thursday that should fewer than 120 deputies of the SYRIZA-Independent Greeks coalition government vote the bailout deal tonight, elections in autumn were unavoidable.

Currently SYRIZA and its Right-wing junior partners jointly hold 162 votes in the 300-member strong chamber. But in the past two critical votes in the assembly in July on the July 13 eurozone summit agreement and the prior actions which opened the way for the third bailout deal, about 40 SYRIZA lawmakers voted against party line.

The tension within the ruling party overshadowed the surprise announcement of the Greek statistics authority ELSTAT on Thursday that in the second quarter of 2015 the ailing economy posted a 0.8 percent of GDP increase compared to the first quarter of the year.

The Greek economy had briefly returned to growth in 2014 but has been severely affected by the uncertainty during the eight month negotiations and the introduction of capital controls since June 29.

Despite the "ray of hope", Greek officials and international lenders expect that the economy will be in recession this year.