Riot police and a small group of protesters clashed in central Athens Friday, on the sidelines of a vigil for the 57 people killed in the country's worst rail disaster. Riot police fired tear gas at a group of protesters who had thrown stones at officers during a rally in Syntagma Square, an AFP reporter said.

Thousands of Greeks protested to demand justice for at least 57 people killed in the country's worst rail disaster, with protesters condemning the tragedy as "a crime".

Some demonstrations turned violent as public anger increased over the role that government mismanagement played in the tragedy. The passenger train ran for several kilometres on the same track as an incoming freight train before the crash, reportedly after the station master in Larissa, central Greece, failed to reroute one of the trains.

It was carrying many students returning from a holiday weekend. Nine young people studying at Thessaloniki's Aristotle University among the dead and 26 others injured. "What happened was not an accident, it was a crime," said student Sofia, 23, who did not wish to give her full name. "We can't watch all this happen and remain indifferent."

The disaster has sparked widespread criticism of government failures in the rail network. Protesters held another series of demonstrations on Friday in the capital Athens and several major cities across Greece. "Most of us knew people who were killed or wounded," said Sophia Hatzopoulou, 23, a philosophy student in Thessaloniki who was visibly angry. It's as if a part of us were lost."

In Thessaloniki -- Greece's second largest city -- police said a protest by about 2,000 people turned violent on Thursday, with demonstrators throwing stones and petrol bombs. Survivors described scenes of horror and chaos when the crash occurred, with many dodging smashed glass and debris as the train toppled over.

Some relatives were still desperately awaiting news of missing loved ones, with a mix of fury and despair. Roubini Leontari, the chief coroner at Larissa's general hospital, told broadcaster ERT on Thursday that more than 10 people were still unaccounted for, including two Cypriots.

Prime Minister Kyriakos Mitsotakis, who is seeking re-election this spring, has blamed the disaster on "tragic human error".

But protests pointing the finger at government mismanagement continued on Friday.

Thousands gathered outside the Athens headquarters of operators Hellenic Train -- which took over network operations in 2017 -- to  protest at decades of failure to improve rail network safety, despite close calls in past years. "Murderers!" the crowd cried out as protesters daubed the word on the building's glass facade in red. Hundreds of people gathered outside the Greek parliament to observe a minute's silence in tribute to the victims of the disaster.

Greece's train services were paralysed on Thursday by striking workers arguing that successive administrations' mismanagement of the network had contributed to the fatal collision. They have urged further strike action. Rail unions say security problems on the Athens-Thessaloniki railway line had been known about for years. The 59-year-old station master at Larissa has been charged with negligent homicide, but his lawyer has argued that other factors were at play.

"My client has assumed his share of responsibility," lawyer Stefanos Pantzartzidis said on Thursday. "But we must not focus on a tree when there is a forest behind it."

ERT reported that the station master had only been appointed to the post 40 days earlier -- and after just three months' training. Audio files were among the items seized during a police raid on the Larissa train station in central Greece, where Tuesday's crash happened, a judicial source told AFP.

For decades, Greece's 2,552-kilometre (1,585-mile) rail network has been plagued by mismanagement, poor maintenance and obsolete equipment.

After the country's transport minister resigned on Wednesday in the wake of the crash, his replacement, Giorgos Gerapetritis, vowed a "complete evaluation of the political system and the state". Safety systems on the line are still not fully automated, five years after the state-owned Greek rail operator Trainose was privatised and sold to Italy's Ferrovie Dello Stato Italiane and became Hellenic Train.