The Spaniard walked away from the incident clutching his left hand but insisted the most important thing was that everyone involved had emerged unscathed.
"I'm okay and it looks like everyone else is okay," Sainz told Sky Sports F1 during the red-flag period.
"That's the main thing because the crash was really scary. We were doing 290-300kph by that point because probably everyone in front of me thought we were racing and suddenly it looks like we were not racing anymore, everyone put their brakes on and by the time I saw everything it was just too late and it was a big crash.
"It was very similar to [the restart in] Brazil last year, but at the back of the grid where I was, it felt like everyone else thought the race was going and we were all flat out until someone realised the race was not on.
"Something to look into because the speed we were going on the main straight is very big. It could have been much worse if someone was sideways on the main straight and I just could have took him.
"I think it is something to learn from here because it is not a nice feeling to do 280kph and find one car almost at a stop."
Sainz was involved in a separate incident on lap one, being tapped by Lance Stroll at turn two and spinning the McLaren back into the pack.
But he acknowledged he was prepared to take risks at the start because of the MCL35's lack of performance so far this weekend.
"I was fighting with a Racing Point," added Sainz. "I had a really good start and I was side-by-side with him. We had a very, very slight contact and all of a sudden I lost the car.
"Up until then it had been a good start. It was a day to take risks because we haven't been very quick all weekend and I was happy to take the risk at the start but unfortunately it didn't quite pay off. The main thing is that we are all okay now."
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