The unusual accident was sparked after Antonio Giovinazzi crashed into the back of Williams driver Nicholas Latifi at the restart following a safety car period.
McLaren’s Carlos Sainz then hit Giovinazzi sending the Alfa Romeo driver temporarily into the air.
Haas driver Kevin Magnussen was also caught up in the accident with all four cars sent into the barriers.
The drivers involved walked away unscathed but Romain Grosjean was furious with leader Valtteri Bottas for driving too slowly at the restart.
👀 A long view and a close-up of the crash that's brought the remaining drivers back into the pits
It's the first time that we've had a Red Flag in consecutive races since 2011 - Monaco followed by Canada#TuscanGP 🇮🇹 #F1 pic.twitter.com/Z2QT1k1ckEAdvertisement— Formula 1 (@F1) September 13, 2020
“That was f****** stupid from whoever was at the front,” the Frenchman yelled over the radio.
“They want to kill us or what? This is the worst thing I have ever seen.”
Bottas had assumed the lead from pole-sitter Lewis Hamilton after the world champion made a poor start.
The safety car was issued after just two corners when Max Verstappen and Pierre Gasly, last week’s surprise winner at the Italian Grand Prix, ended up in the gravel.
It meant that by the end of lap nine, six drivers had retired from the race with the red flags out for the second grand prix in as many weeks. Formula One is racing in Mugello for the first time to mark Ferrari’s 1,000th Grand Prix.
