Violent street clashes erupted in Athens as tens of thousands demonstrated during a nationwide strike against the cash-strapped government's austerity measures.

Hundreds of masked and hooded youths attacked police and were met with volleys of tear gas and stun grenades.

The violence spread after the end of the march to a nearby square, where police were faced by stone-throwing anarchists. Suffocating clouds of tear gas sent customers running from open-air cafes.

Police say 16 people were detained and two officers were injured.

Rioters used sledgehammers to smash the windows of more than a dozen shops, banks, jewellers and a cinema. Youths also set fire to rubbish bins and a car, smashed bus stops, and chopped blocks off marble balustrades and building facades to use as projectiles.

Organisers said 60,000 people took part in the protest. But an unofficial police estimate set the crowd at around 20,000 -- including those that took part in a separate, peaceful march earlier.

The strike -- the second in a week -- brought the country to a virtual standstill, grounding all flights and bringing public transport to a halt.

State hospitals were left with emergency staff only and all news broadcasts were suspended as workers walked out for 24 hours to protest at spending cuts and tax rises designed to tackle the country's debt crisis.

Riot police made heavy use of tear gas during the start-and-stop clashes throughout the demonstration, including outside Parliament.

Strikers and protesters banged drums and chanted slogans such as "no sacrifice for plutocracy," and "real jobs, higher pay." People draped banners from apartment buildings reading: "No more sacrifices, war against war."