Greek police clashed with protesters on Wednesday as around 100,000 workers, pensioners and students marched to parliament in protest at austerity policies aimed at helping Greece cope with a huge debt crisis.

Riot police fired tear gas and flash bombs at protesters hurling petrol bombs, stones and bottles in the main Syndagma square in Athens.

A 24-hour strike by public and private sector employees grounded flights, shut down schools and paralysed public transport in this year's first nationwide walkout against cuts.

In the biggest march since the December 2008 riots brought the country to a standstill for weeks, about 100,000 Greeks marched through the streets of Athens.

Shops barricaded their windows and hotels in central Athens locked up.

Police said two policemen and five civilians were injured, including one journalist hurt by a petrol bomb. Four protesters were detained.