The accident left the two seriously injured, reported the Bangkok Post.
The woman, identified as Walailuck Sukama, 28, had her right leg severed after being dragged and left beneath the passenger train.
The man, identified as Amnaj Nawantib, 25, suffered head injuries after being knocked off the track, leaving him unconscious.
Both were promptly rushed to Vajira Hospital in the Thai capital.
Their friend, Amornthep Tipnongwaeng, 25, told police the three of them had been drinking alcohol in the area for an hour before making their way down to the railway tracks at 4am.
They wanted to take selfies with an outbound train that was on the other set of tracks, reported The Nation.
However, they were too late to notice another train that was approaching the station along the tracks they were taking photos on. Their failure to notice the train has not yet been ascertained.
Police captain Wisanusak Sueb-in, deputy inspector of Samsen Police Station, was alerted to the accident at 5am.
Mr Wisanusak commented that police will interrogate the train driver, the two victims and witnesses of the accident. Surveillance camera footage of the area will also be examined.
The police have yet to decide if charges will be filed.