Greece has seen a series of strikes and violent protests since austerity measure were announced in summer [AFP]

Striking public and private sector workers in Greece have grounded flights, shut down schools and paralysed public transport.

Clashes erupted between police and protesters in Athens, the Greek capital, as demonstrations take place against a new wave of austerity measures.

Greek police fired teargas at protesters who threw petrol bombs at two hotels in a square outside parliament, setting one balcony alight while others set cars ablaze.

Windows of shops and a private college were smashed by rock-throwing youth who also set fire to piles of garbage that had accumulated in the city centre due to rolling strikes by municipal rubbish collectors.

Protesters broke off pieces of marble from balustrades which they used as projectiles to attack riot officers. Police said nine people were arrested and another 11 detained, while three were injured.

An estimated 15,000 people turned out at Syntagma Square on Wednesday, police said, hours after parliament approved a bill that will cut the salaries in public utilities.

A former conservative minister was attacked by a group of about 200 activists with sticks and stones. Kostis Hatzidakis sought refuge in a nearby building with his face covered in blood, a witness said.

The government condemned the attack, saying that Greek democracy "cannot be muzzled or terrorised."

Another 20,000 people joined a protest in the northern city of Thessaloniki earlier in the day, which also resulted in violence when youths hurled firebombs at a central government building and vandalised several banks and stores.

Bleak outlook

Barnaby Phillips, Al Jazeera's former Athens correspondent, said "things are coming to a crunch in Greece".

"Many of the austerity measures which were announced during the spring and the summer have been somewhat delayed in their effects.

"It's really now that ordinary Greeks are feeling the pain," he said. "Unfortunately the outlook for the country remains very bleak.

"Economists think that during 2010 [the economy] would have shrunk a little bit over four percent but it will continue to contract throughout 2011 by perhaps another three per cent, so there isn't really light at the end of the tunnel yet."

Previous spending cuts brought in by the government, under an agreement by the European Union and International Monetary Fund, which approved a joint bailout for debt-stricken Greece, had triggered mass protests and strikes.

Wednesday's action comes as workers prepare to rally against austerity measure in other European countries on Wednesday, including Spain, France and the UK.

In Brussels, the Belgian capital, hundreds of protesters formed a human chain around the European Commission to denounce spending cuts undertaken by governments across the region.

Up to 300 people circled the glass building, holding banners reading "no to austerity, priority to jobs" and "no cuts to public spending".

The action comes on the eve of a two-day summit on the European debt crisis.