“The driver slammed the brakes just before we crashed. People were tossed forward in the carriage. There was smoke and people panicked,” one witness told local paper Göteborgsposten (GP).

Another witness said the collision sounded like an explosion and described how the carriages were lifted up by the crash.

“It wasn’t until we got out that we saw how serious the crash had been,” said passenger Evelina Fredin to Sveriges Radio (SR).

Out of the 28 taken to hospital 23 could go home shortly after, leaving five in need of further medical treatment.

The reason behind the accident is still unknown.

According to several witnesses the number 6 tram was at the station as the 11 drove in to the back of it.

The driver was one of the 28 taken to hospital and police have had no chance to question him yet.

“Our investigator will most likely question him during the course of Saturday,” said Christer Olsson of tram company GS Spårvagn.

According to Olsson, investigators are also gathering witness statements and examining the trams for any other clues as to why the collision occurred.

So far there are no indications that the driver blacked out, fell asleep or was disturbed while driving.

“This is what the investigator will have to try to establish. I don’t really have a theory into what happened or why,” Olsson told GP.

According to Olsson collisions are known to happen from time to time but he can’t recall any previous incident when they have collided at this speed.

The driver who is described to be in his forties is expected to be well enough to be questioned over the weekend.

Having worked as a tram driver for a year he has reportedly been a bus driver for many years prior to that.

“It was terrible. I have been crying incessantly since it happened,” said 21-year-old Elise, a passenger aboard one of the crashed trams, to GP four hours after the incident.