Rain over the Spa-Francorchamps circuit between the end of Qualifying 2 and the start of the session's final segment saw conditions rapidly deteriorate.
Though the session began on schedule – albeit 12 minutes late owing to the delay starting the 60-minute session – it was quickly halted with a red flag.
On his out lap from the pits, Vettel had complained about the conditions to the team, stating the red flag should be shown.
Ahead of him on the road, Norris shared similar concerns, relaying concerns about aquaplaning.
Shortly after beginning his first flying lap of the session, Norris crashed heavily after losing control at the Raidillon right-hander.
Vettel was the first driver on the scene and was greeted by debris strewn across the circuit and the McLaren stationary in the run off.
“It's always easy afterwards but the main thing is that we learn from what happened,” Vettel said.
“It could have been a different outcome with the crash, so I think we got lucky that nothing bad happened.”
The four-time world champion revealed he realised conditions were too wet shortly after leaving the pits, with the Kemmel Straight which follows Raidillon especially bad.
While the German shared his thoughts with the team, he stopped short of being overly critical of race control's response to his calls for the red flag.
“I think they do,” he said when asked if race control should listen to the drivers.
“We are feeding it back as a team to the race control, but there's a lot of drivers, a lot of teams, so it's a lot of radio and you cannot be listening to everybody at every time.
“It is clear that we should not have gone green.”
Having received a signal from Norris that he was indeed okay, Vettel returned to the pits and waited out the stoppage before recording a time that will see him start the race from fifth.
They quickly realised their error and switched, recording the second- and ninth-fastest times respectively.
“The trouble is that the extreme wet has a super small working window,” Vettel said, explaining why most opted for the green-walled intermediate rubber despite the potential risks it posed.
“It's not great when there's a lot of water but then very quickly when the water disappears, I mean, we have cars that suck the water off the track very quickly with the ground effect that we have nowadays, and that pushes to an Inter because the intermediate is a lot faster.
“So that's why everybody's rather taking a ride on the knife's edge with an intermediate because the reward is much greater.”
Norris walked away from the crash, first to the circuit's medical centre before being cleared to race following further checks at a nearby hospital.
The Belgian Grand Prix, which is forecast to be wet, gets underway at 23:00 AEST tonight.