Youths hurled rocks and fire bombs at riot police in central Athens to protest against new cost-cutting measures being debated in Parliament.

For several hours, police fired repeated volleys of tear gas and stun grenades at masked and hooded youths just before the second day of debating was to resume.

Police said 18 people were detained, with five of them later arrested, while four policemen were injured and transferred to a military hospital.

The latest austerity measures must pass in two parliamentary votes Wednesday and Thursday if Greece is to receive another batch of bailout funds to see it beyond the middle of next month. If the votes don't pass, Greece could become the first eurozone nation to default on its debts, sending shock waves through the global economy.