Tens of thousands of people gathered in Athens in a demonstration to mark the second anniversary of a rail accident that killed 57.

Greek riot police deployed tear gas and stun grenades to disperse a smaller group of protesters throwing Molotov cocktails and stones.

Protesters have alleged that the government was involved in a cover-up of evidence, slowing down investigations into the crash.

What do we know about the protest?

Over 170,000 people attended the protest in Athens, and some 325,000 people in total took to the streets nationwide, according to police.

A total of 5,000 police officers have been deployed in the capital.

Police said that between 500 and 700 people were involved in riots. Police arrested over 80 individuals.

Riots also broke out in Greece's second-most populous city of Thessaloniki.

Greece's ambulance service said some nine people were taken to hospital, including a photographer that had been hit in the head by a stun grenade.

Strike, shop closures accompany demonstrations

Alongside the protests, private-sector unions kicked off a 24-hour general strike, which paralyzed public transport and caused the closure of government offices and schools.

Shops and businesses across the country also closed for several hours.

GSEE, the biggest private-sector union, said it had called the strike "so that the rule of law can finally be implemented; so that there is no cover-up; so that those responsible are punished."

What was the Tempi railway disaster?

Protesters on Friday marked the second anniversary of the Tempi railway disaster, in which a passenger train from Athens to Thessaloniki collided with a freight train.

57 people died in the crash, including many students, and many more were injured.

The two trains had traveled toward each other for miles without triggering any alarms.

Polls indicate that between 70-80% of Greeks believe that the government was involved in a cover-up of evidence suggesting insufficient safety measures.

An experts' report funded by victims' families has claimed the freight train was carrying an illegal and unreported load of explosive chemicals. The Hellenic Train operator has denied knowledge of any illegal cargo on the train.

The government has denied allegations of a cover-up and Prime Minister Kyriakos Mitsotakis has dismissed calls to resign, accusing critics of attempts to "destabilize" the country.

Greece's opposition parties are set to call a no-confidence vote next week.

Edited by: Rana Taha