Rail traffic will resume "gradually" in Greece from March 22 as the country reels from its deadliest train crash, the transport minister said on Tuesday.

Fifty-seven people, many of them students, were killed when a passenger train and freight train collided head-on in central Greece on February 28.

Rail traffic, halted after the incident at Tempe, 350 kilometres from Athens, "will gradually resume from March 22," Transport Minister George Gerapetritis said. 

Four railway officials have been charged, but public anger has focused on long-running mismanagement of the network and the country has been rocked by a series of sometimes violent mass protests.

On Sunday, about 12,000 demonstrators gathered outside parliament, while 5,000 took to the streets of the second city Thessaloniki, police said. 

"We're getting desperate. You don't know what to say, what to do - all you can do is join the protest," 26-year-old demonstrator Alexandros, who only gave one name, told AFP Sunday. 

 Accusations

In Athens, at least two protesters could be seen carrying a placard that read "murderers" among the thousands who marched through the streets Sunday.

One of the biggest protests saw tens of thousands demonstrate nationwide last Wednesday, with clashes erupting, while civil servants from doctors to transport workers staged strikes. 

Prime Minister Kyriakos Mitsotakis, who is fighting to be re-elected within months, has faced calls from some protesters to quit. 

He has come under fire for initially pointing to "human error" for the accident and blaming the station master on duty at the time, who allegedly routed the trains onto the same stretch of track by accident.

But railway unions had long been warning about problems on the creaking, understaffed train network.

Main opposition leader Alexis Tsipras has also accused the government of not paying any heed to their repeated warnings over the past two years.

The station master is among the four railway officials who have been charged.

Greece's previous transport minister resigned after the crash and Mitsotakis has sought to soothe public anger by repeatedly apologising and vowing a transparent probe.