Heidi Langberg Zumbusch, who had just boarded the train and taken her seat when the accident happened, said there was a "loud crash and the windows started smashing onto our heads".
Images from the scene show containers on the freight train with their sides torn off.
The Storebaelt bridge is part of a fixed link between the islands involving bridges and tunnels. "It has been a pretty serious accident".
Six people were killed on Wednesday (Jan 2) after debris apparently from a cargo train smashed into a passenger train in high winds on a bridge connecting two islands in Denmark, the rail operator and officials said.
Danish police suggested that cargo from the freight train fell off and hit the passenger train, reported Associated Press news agency.
Danish Prime Minister Lars Lokke Rasmussen said the tragic accident "has shaken us all".
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An accident response centre has been set up in Nyborg on Funen, and DSB has confirmed that the Havarikommissionens accident investigation unit and Funen Police will investigate the cause of the accident. Also damaged was the freight train, which was carrying a load that included crates of Carlsberg beer.
A witness said survivors had to step over dead bodies in order to escape.
The bridge has now reopened to road traffic heading east but with speed restrictions in place, police said.
The 18-kilometre long bridge across the Great Belt carries around 21,000 train passengers every day and more than 27,000 vehicles crosses the bridge each day.
Denmark's Queen Margrethe said the "terrible accident ... touches me deeply". Police did not provide further details about those killed or the number of people injured in Wednesday's incident, which took place about 8 a.m. local time.
Denmark's worst train accident occurred in 1919, when an express train collided with a stopped train in Copenhagen due to a dispatcher error.