Walls received treatment for more than 40 minutes before being taken away by ambulance, with spectators also hurt after he and his bike had come over the top of the barriers on the high banking of the corner.
The 24-year-old Olympic omnium champion was trying to avoid riders who had fallen in a crash lower down the banking but as he rode up, he clipped another wheel and went over the top.
Witnesses said that, because of the gradient of the banking, spectators in the front row had been unsighted for the crash. One man received treatment for cuts to his arm while a young girl also received minor attention.
The remainder of the morning session at the velodrome was cancelled and spectators were asked to leave as medical staff attended to Walls.
More to follow.