Police used tear gas after demonstrators hurled stones and firebombs, news agencies reported.
The unrest took place amid a nationwide strike that halted train and ferry services, canceled most flights and shuttered schools and businesses, and which has been organized by workers and their unions under the banner "Their Profits vs. Our Lives."
Protesters demanded accountability for the 2023 collision, alleging negligence and safety lapses by authorities.
Surveys show most Greeks believe officials have withheld key information about the tragedy, whose investigation remains ongoing.
'Far-right voices gaining strength through these events': expert
Speaking to Polish state news agency PAP, political scientist Stella Ladi from Athens’ Panteion University said that "radical forces" are trying to leverage public anger for their own ends.
"The situation is being instrumentalized to get people onto the streets," she said, noting that the demonstrations also express growing frustrations over rising prices and uncertainty.
"Protesters often don’t realize that far-right voices are gaining strength through these events," Ladi added.
Prime Minister Kyriakos Mitsotakis urged unity, cautioning that "some want to transform collective mourning into a chance for further divisions."
He pledged the government would avoid a repeat of the train disaster while acknowledging "mistakes and failures" in handling the aftermath.
Opposition parties, meanwhile, have called for a no-confidence vote, citing "systemic errors" that led to the deadly collision between a freight and a passenger train near Larissa, northern Greece, on February 28, 2023.
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Source: IAR, PAP, Sky News