The two companies had worked together to promote the event.
The man who died was on the raft that overturned at the "Toilet" rapid around 3.45pm, they said.
The rapid was about three quarters of the way through the rafting trip.
The two outfits said rafts overturning was not unusual for grade 4 to 5 rivers.
"It was as one of the rafters was being brought back from the far side of the river using a rescue rope, that he lost his grip."
The man was swept through the rapid and met by a safety kayaker who helped him navigate the next rapid before assisting him to the shore.
"He became unresponsive, CPR was provided and a defibrillator utilised.
"The guest received further treatment from paramedics who arrived by helicopter just after 5pm but was unable to be resuscitated."
Yesterday was a fine, sunny day and river conditions were "considered medium to low flow at 16 cubic metres per second which is well within standard operating parameters".
Queenstown Rafting General Manager Luke Taylor said he and his staff are devastated by the incident.
"Our hearts go out to our guests and the families of those involved in this. Both our companies wish to offer the group our sincere condolences and ongoing support."
It came two months after the death of one of its guides on the same stretch of river following a medical event.
In March, "well loved and highly respected" whitewater rafting guide Keith Haare
died in the Shotover River after his raft overturned with other people on board.
Taylor said at the time the passengers on the raft were all unhurt and made it to the shore safely, but the company's guide was found unresponsive in the water after attempting to right the craft.