Bamber was pressuring Neel Jani's Proton Porsche 963 LMDh for third place with a little under two hours remaining in the race when the pair came upon the battle for fourth in the LMGT3 class on the run to Les Combes.
With Jani delayed slightly behind Gelael's WRT-run BMW M4 GT3 and the D'Station Aston Martin Vantage of Erwan Bastard, Bamber had a run on the Swiss rounding the Kemmel Straight's right-hand kink.
But as he moved to the right in a bid to draw alongside Jani, he clipped the front of Gelael's car and speared his own Chip Ganassi Racing V-Series.R LMDh hard into the barriers on the right-hand side of the road.
Bamber's car became airborne before landing on its wheels, while Gelael made heavy contact with the barriers on the left-hand side.
Both drivers are understood to be okay.
With minutes left on the clock before the original six hour duration was set to elapse, it was announced that the race would be extended by the same 1hr47m duration of the red flag.
The race is set to resume at 19:10 local time
(DRIVERS OK) Here is the accident that caused the red flag.#WEC #6HSpa pic.twitter.com/O9dY98Harr
— FIA World Endurance Championship (@FIAWEC) May 11, 2024
"It could have been a lot worse, I think I'm quite lucky here," Gelael told the WEC's live feed.
"I was just in the middle, the two guys were fighting in front and they misjudged and sometimes the misjudgement can lead to bigger things. I think everyone else sees.
"We were going to salvage something this weekend, anyways we didn't, but hopefully for Le Mans, it's the big one that I hope it doesn't happen in Le Mans. Fingers crossed, full focus there.
"But it's also an accident you shouldn't take lightly. I understand these things happen and it's part of racing, but it's also something I think very avoidable.
"The respect given between categories and the respect between drivers; some people do it very well, and some people do it a bit less. Today was the worst part."
WRT's LMGT3 team manager Kurt Mollekens said: "It's very unfortunate, one weekend is not the other. We were the heroes of the previous one, now we go back with zero points both cars, big crashes, a lot of work to do before Le Mans.
"We would have preferred to avoid it like everybody else would, but it is what it is.
Ferrari was leading the race at the time of the stoppage with its pair of factory-run 499P Le Mans Hypercars.
Alessandro Pier Guidi in the #51 entry was leading Antonio Fuoco in the #50 car that was disqualified from qualifying for running underweight and had been demoted to the back of the grid.
Both had overtaken the privateer Proton Porsche that had led in Jani's hands at half-distance, despite a bizarre problem with his door-hatch.
Shortly after taking over the lead from Julien Andlauer under a virtual safety car, the Swiss spent several slow laps trying to close his reluctant door and was shown a black and orange flag before managing to pull it shut.
The Bamber-Gelael crash was the second major incident of the race, with the VSC triggered by BMW driver Rene Rast tagging the back of Phil Hanson's Jota Porsche on the run to Bruxelles and spinning it into the path of Ahmad Al Harthy in the other WRT BMW GT3.
Both Hanson and Al Harthy retired, while Rast's car was ordered to serve a drive-through penalty.
Repairs to the armco barriers meant the race remained under caution for almost an hour before resuming.
The LMGT3 class is currently led by the Manthey EMA Porsche of Morris Schuring, who was shortly due to hand over to Richard Lietz.
