One person died at the scene. Several others were taken to Sundsvall Hospital to be treated for injuries, one of whom later died from injuries sustained in the accident.
The collapse occurred when a mould gave way at Saltviksstrand at the southern end of the 770 metre long bridge.
"There were five people involved in the fall. They fell around fifteen metres to the ground," said Ola Nilsson, a spokesman for the Swedish Rail Administration (Banverket).
It is not yet clear where the construction workers involved were located when the accident took place.
Building work on the bridge is being carried out by Skanska. The workers involved were employed either by the construction giant or by sub-contractors brought in by Skanska.