The Tuscan Grand Prix was red-flagged after nine laps following a scary pile-up involving four cars at a Safety Car restart.
On Lap 8 the Safety Car came into the pits, allowing race leader Valtteri Bottas to manage the pace out in front and decide when to hit racing speed. The Finn waited until the start-finish line before accelerating, as he is allowed to under the rules.
That caused a bottleneck effect behind him and at the back of the field Antonio Giovinazzi and Nicholas Latifi appeared to hit racing speed before anyone else did. Latifi quickly came across Haas' Kevin Magnussen, who was following the pace of the cars in front, and swerved out of the way -- Giovinazzi was unable to do the same and went into the back of Magnussen's car.
McLaren's Carlos Sainz had also started accelerating and hit that crash ahead of him, briefly pushing Giovinazzi's car onto its side and into Latifi's Williams.
The incident prompted the red flag, the second race suspension in two weeks after last weekend's Italian Grand Prix was red-flagged at mid-distance when Charles Leclerc crashed out.
Haas' Romain Grosjean managed to get through the pile-up without race-ending damage, but he was furious with how the incident played out, suggesting the blame should lie with the driver dictating the pace at the front.
Immediately after the incident, Grosjean shouted over the radio: "That was f---ing stupid from whoever was at the front. They want to kill us or what? This is the worst thing I have seen ever."
McLaren's Sainz ploughed into the back of Giovinazzi and Magnussen.
When Sainz got out of his car, he was holding his left hand, although he later confirmed to Sky Sport he was OK.
"Properly scary," Sainz said afterwards. "We're doing 290, 300 kph at that point, because everyone in front of me just thought that we were racing. Suddenly it looks like we were not racing anymore and everyone started braking again. By the time I saw everything it was just too late and it was a big crash.
"It felt like at the back of the grid where I was everyone in front of me thought that the race was going and we were all flat out until someone realised the race was not on. Something definitely to look into because the speeds we are going at the main straights are very, very big so the crash I had could have been much worse if one car would have sideways on the main straight and I could have took him.
"It's something to learn from here because it's definitely not a nice feeling to do 280 kph and suddenly find three cars in the middle of the straight just stopped."
It left 13 out of 20 cars in the race for the restart -- Monza race winner Pierre Gasly and Red Bull's Max Verstappen were out of the race after tangling on Lap 1. Renault's Esteban Ocon retired from the race during the red-flag stoppage.
The 59-lap race restarted at 14:00 local time.