Greece's conservative government was hit with a censure motion in parliament on Tuesday over claims that it sought to manipulate an ongoing investigation into the nation's worst train tragedy.

The motion lodged by the socialist PASOK party, and backed by other opposition parties, is unlikely to succeed as the government has an absolute majority in parliament.

PASOK chairman Nikos Androulakis said the motion had the support of three other leftist parties and declared that Prime Minister Kyriakos Mitsotakis "has no choice, he will come here to justify his actions."

A vote of confidence will be held on Thursday evening after a three-day debate.

The disaster that killed 57 people in February 2023 struck when a freight train and a passenger train with 350 staff and passengers, mostly students, collided near a tunnel outside the central city of Larissa shortly before midnight.

A year after the accident, relatives of the victims say that despite government promises of a full investigation, state authorities wasted time and overlooked vital evidence.

Experts appointed by relatives' families say the accident site was cleaned of wreckage and topsoil before investigators could fully examine it.

The body of a young woman travelling on the train still remains unaccounted for, and there are claims the freight train was carrying undeclared chemicals.

A Metron Analysis opinion poll last week found that almost nine in 10 Greeks thought little progress has been made in the investigation.

On Sunday, there was further anger after the To Vima weekly reported that leaked recordings of train staff on the night of the accident, played by media at the time, had been edited to suggest human error was exclusively to blame.

Opposition parties subsequently accused the government of "handing out" the edited recording to friendly media, to bolster its narrative that human error caused the collision.

Critics point to an address to the nation by Mitsotakis just hours after the accident, in which he said that "everything" showed human error was to blame.

The government has reacted with fury at the claims, calling opposition parties "grave robbers" aiming to "destabilise" the country.

Government spokesman Pavlos Marinakis called the To Vima report "baseless" and a "stain" on the newspaper's history.

Main opposition party Syriza has called on Mitsotakis, who was comfortably re-elected in June, to resign.

The government, which has 158 lawmakers in the 300-seat parliament, welcomed the no-confidence vote.

Opposition parties were already furious this past week after a four-month parliamentary investigation into the accident concluded without assigning blame to senior politicians.

Over 30 railway employees and officials face charges over the February 28, 2023, disaster, with a trial expected to start in June.

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

The government last year shrugged off another censure motion over a wiretap scandal implicating state intelligence and the prime minister's office.