VANCOUVER -- Police are investigating an incident at Columbia SkyTrain Station in New Westminster that a witness says involved a woman being hit by a train Thursday evening.

TransLink initially described the situation as a "medical emergency" in a tweet shortly after 6:20 p.m. and in a news release shortly before 7.

The transit authority said Expo Line trains were stopping and turning back at New Westminster, Braid and Scott Road stations, and a bus bridge was set up to help passengers get between the three stations.

Mike Tumu was on the platform at the time of the incident. He told CTV News Vancouver that two people who appeared to be intoxicated were having an argument.

The woman was striking the man, who was blocking her punches in self-defence, Tumu said. He said the woman attempted to hit the man as a train was pulling into the station, but she tripped and fell onto the tracks.

Tumu said it did not appear to him that the woman was pushed. The man remained on the platform, seemingly in shock, the witness said.

"Everybody was shocked," Tumu said. "People were screaming, people were crying. We all thought she was dead. Fortunately, she's not."

He said he saw the victim taken out on a stretcher while he was waiting to speak to police about the incident.

"By some magical miracle, she's out on a stretcher and her arms are moving," Tumu said.

Reached by phone, Metro Vancouver Transit Police referred questions to the New Westminster Police Department, which transit police said is leading the investigation.

A spokesperson for NWPD described the situation only as "a police incident," and said more information would be provided in the morning. He said he expected the station would be closed for three or four hours as police investigated.