Clashes have broken out in Athens during a general strike called across Greece in response to a rail disaster last month.
Protesters hurled petrol bombs at a police cordon near parliament.
Riot police responded with tear gas and stun grenades during the brief flare-up of violence that disrupted large, peaceful demonstrations.
There were no immediate reports of injuries or arrests.
The strike grounded flights and extensively disrupted services, while large protests were also held in other cities across the country.
Clashes between youths and police also erupted in the southern port city of Patras.
The strike kept ferries to the Greek islands in port, left hospitals running with emergency staff, halted public transport services and led to class cancellations at state-run schools.
Unions have rallied behind railway workers’ associations which have staged rolling walkouts since the head-on train collision in northern Greece on February 28th that left 57 people dead and dozens injured.
“This government has had four years to fix problems with the rail network, but instead of owning up to that responsibility, they are blaming everyone else,” Popi Tsapanidou, a spokeswoman for main leftist opposition party Syriza, told private Skai television.
The main protests were held in Thessaloniki, Greece’s second-largest city, and in the capital Athens, where thousands chanted “this crime will not be forgotten”.
Stores and banks lowered their shutters when the protesters filed past as the capital was brought to a standstill.
A wide variety of labour associations — from those representing lawyers to delivery drivers — joined the strike.
The government, which faces a parliamentary election before the summer, says rail services will restart on March 22nd and will be restored gradually until April 11th, with additional staff to monitor safety and mandatory speed reduction rules along sections of the track.
Greek prime minister Kyriakos Mitsotakis’s centre-right government has seen a strong lead in opinion polls reduced in recent weeks over its main rival, Syriza, with the two sides also locked in an ideological debate over how to reform Greece’s antiquated rail network.
Mr Mitsotakis has promised clearer boundaries between privatised services and the authorities overseeing them, seeking assistance from European Union experts in drawing up the changes.
His political opponents argue that the poorly managed dismantling of agencies under state control has compromised rail safety.
