Death toll from Greece train crash rises to 57, three-day national mourning until Friday declared

The death toll from Tuesday night's train crash in central Greece has increased to 57, authorities said on Thursday.

Forty-eight people remain hospitalized, six of them in intensive care, Greek police spokeswoman Konstantia Dimoglidou told journalists.

A search and rescue operation is expected to conclude on Friday, Greek Fire Service spokesman Vasilios Vathrakogiannis added.

An investigation is simultaneously underway to determine the causes of the crash -- how and why a passenger train collided head-on with a freight train traveling in opposite directions.

A station master has been arrested and charged with manslaughter by negligence.

The government has declared a three-day national mourning until Friday and promised that problems affecting the operation of railways will be addressed to prevent such tragedies in the future.