This is the heroic moment a quick-thinking guard saved a pensioner from an oncoming train.

The railway officer was holding a green flag to signal that the track was clear for the train when the elderly man suddenly attempted to cross in Samut Sakhon, Thailand.

Footage shows the locomotive's horn blaring at the pedestrian in a red shirt, prompting the crossing keeper to yank him to safety just seconds before it sped past on July 8.

The guard then pushed the man back behind the boom gate, sternly scolding him for the reckless attempt.

Railway guards are stationed at certain level crossings in Thailand as part of State Railway safety measures, particularly at high-risk locations where pedestrians or vehicles might ignore warnings.

Last year in June, a woman was struck and killed while walking across the tracks near Bang Sue Junction. Witnesses said she attempted to cross despite the train's warnings.