Thousands of protesters have taken to the streets of Athens and Thessaloniki to express anger at new pension and tax-break cuts forced on Greece by its EU-IMF creditors in return for bailout funds.

Wednesday's walkout cut off maritime traffic for a second day while dozens of flights had to be cancelled or rescheduled and hospitals ran on emergency staff.

Nearly 12,000 people turned up for the protests in Athens and another 6,000 in Thessaloniki, according to police, a day before the measures were to be approved by parliament.

Police used tear gas on a small group of youth that threw petrol bombs and fired flares in Athens.

Nearby, police officers who were part of the protest blocked the entrance to a finance ministry building.

Police unionists displayed a giant banner on the side of Lycabettus Hill in the centre of Athens, with a slogan in German and Greek reading "How much is the life of a Greek policeman worth?"

The bill, to be approved on Thursday night, entails $5.4bn in cuts from 2018 to 2021, Greek state agency ANA reported.

Unless bailout funds are unlocked, Greece would once more struggle to meet an increase in debt repayments due this summer and face another possibility of bankruptcy.

Greece hopes that the new loan payment will be approved by a meeting of euro zone finance ministers on May 22.

In parliament, legislators were debating the measures that include additional pension cuts in 2019 and higher income tax from 2020.

The government, which originally came to power in 2015 promising to repeal previous austerity measures, has emphasised it will also take other measures to relieve poverty.

On Tuesday, Alexis Tsipras, Greek prime minister, spoke to German Chancellor Angela Merkel, whose country has been the single largest contributor to the Greek bailouts, and discussed the issue of Greece's debt, his office said.

While Greece's finances have improved under the rescue plans, the austerity has led to a rise in poverty.

Unemployment, while down from highs of above 27 percent, hovers at around 23 percent.