The Football Association of Wales confirmed that no players or staff were injured in the incident, which also involved another vehicle.
Emergency services were on the scene and, although an ambulance attended, all parties were reported to be unharmed.
Head coach Rhian Wilkinson and captain Angharad James, who were travelling separately, were not on board.
Speaking at a press conference as news filtered through, Wilkinson said: "I think everyone, from all reports, is OK and we just need to get them all together and get everyone away from the scene to reassess."
She added that the well-being of everyone involved was the priority: "Football is secondary... we are shaken because we are away from the team right now, knowing that they've had to experience that."
"Our priority is to get them all together and away from the scene. We'll be checking in to make sure they all continue to be ok.
"This is really developing right now, so we are trying to be as clear and transparent as possible.
"More importantly, I think the driver of the other vehicle is ok as well. We will let everyone know once we know for sure."
The scheduled training session was cancelled as a result.
"The Football Association of Wales can confirm that the Cymru national team bus has been involved in a road traffic accident whilst travelling to Arena St Gallen for their matchday training session ahead of Wednesday's UEFA Women's Euro 2025 match against France," an FAW statement said.
"All passengers on the Cymru national team bus and in the other vehicle are unharmed.
"The FAW's priority has been to remove the players from the scene and return to the Cymru training base to complete their preparations for tomorrow's match."
The timing could hardly be more unfortunate. Wales are already under pressure following a 3-0 defeat to the Netherlands in their Group C opener.
Another loss against France would almost certainly end their hopes of reaching the knockout stages before their third match against England.
With emotions understandably heightened, the Welsh squad must now refocus both mentally and physically in what has become an even more daunting challenge.