With the race starting under heavy rain, Gasly had collected a piece of advertising barrier and pitted at the end of lap one as a safety car was deployed to allow Carlos Sainz's stricken Ferrari to be cleared away following a crash.
The race was then delayed as conditions worsened, but as Gasly attempted to catch the other drivers, he passed a recovery vehicle that had been sent out without the knowledge of the drivers.
"I could have killed myself," Gasly fumed as he spoke to his pit wall with the race restart delayed.
"What is this tractor on track?" he shouted on team radio. "I passed next to it. This is unacceptable. Remember what has happened. Can't believe this."
Other drivers were unhappy that they had not been informed of the tractor being on the circuit, with Sebastian Vettel saying: "Next time, they should inform us if there's a frickin' tractor on the road. I know we're under Safety Car, but in turn 12, there's this…"
The FIA issued a statement on the location of the recovery vehicle: "In relation to the recovery of the incident on Lap 3, the Safety Car had been deployed and the race neutralised.
"Car 10, which had collected damage and pitted behind the Safety Car, was then driving at high speed to catch up to the field.
"As conditions were deteriorating, the Red Flag was shown before Car 10 passed the location of the incident where it had been damaged the previous lap."
Sainz said: "Still behind the safety car, we're going at 150kph, and still we cannot see anything."
"If a driver has small aquaplaning, or gets out of the racing line, and hits a tractor, it's over."
"Why risk a tractor on track? They were going to red flag anyway."
Gasly was summoned by the stewards under an alleged breach of speeding under red flag conditions, while McLaren's Lando Norris tweeted: "Wtf. How's this happened!? We lost a life in this situation years ago. We risk our lives, especially in conditions like this. We wanna race. But this… Unacceptable."
The incident came at the same venue where Bianchi crashed in 2014 under similar conditions, the Frenchman ploughing into a tractor that was recovering another car that had gone off at the same corner and dying of his injuries the following year.
Bianchi's father posted on Instagram, circling the tractor in Gasly's eyeline and adding the caption: "No respect for the life of the driver no respect for Jules memory incredible."
Red Bull team principal Christian Horner feels a full investigation needs to be carried out.
He told Sky Sports: "It is totally unacceptable. We lost Jules Bianchi here and that [a recovery vehicle on track] should never ever happen so there needs to be a full investigation why there was because it obviously shouldn't have been… it is extremely dangerous. We've got lucky so far."