Alonso’s right wheel clipped Esteban Gutierrez’s Haas at high speed going into turn three of the 18th lap and the impact sent the Spaniard’s McLaren careening into a barrier, smashing it to pieces, before it flipped, rolled and flew end-over-end into another barrier.
The two-time world champion emerged from the wreckage and walked gingerly over to Mexican Gutierrez where the pair embraced.
“We believe he’s OK. I’m sure his marbles are rattled a little bit,” McLaren chairman Ron Dennis told Sky Sports.
The race was suspended as track staff swept debris away, bringing the rest of the cars back to pit before it resumed at 4:55 p.m. local time (0555 GMT) following a lap with the safety car.
Race control said the incident would be investigated.
Haas boss Gene Haas told Sky Sports: “It looked like Alonso was trying to overtake Esteban and just got squeezed and ran out of room and the tires made contact and Alonso went for a hell of a ride.”