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 Formula One world champion emerged from the wreckage and walked gingerly over to Mexican Gutierrez, where the pair embraced.
"I'm okay, I'm trying to put everything in place again," the 34-year-old told Sky Sports in the paddock after Nico Rosberg won the race for Mercedes.
"It was a scary crash. Lucky to be here and happy to be here, and thankful to be here -- especially to the (governing body) FIA and all the safety, thanks to that probably I'm alive.
"We lost the power unit and the car because there was a lot of damage, but I'm super happy to be talking."
Race control said Alonso's contact with Gutierrez would be investigated but the Spaniard said neither driver was to blame.
"We were racing, I kept in the slip-stream as late as I could and at the last moment I tried to move.
"It's tough, you can only see the rear wing, you don't have the full view of the track. And same for him, he's defending and can't see what the other guy is doing. So we are both happy."
Alonso (left) and Gutierrez after the crash. - AFP
It was a disappointing day all round for McLaren, with Alonso's team mate Jenson Button finishing 14th out of the 16 finishers.
Nico Rosberg won the dramatic race for Mercedes after Ferrari's challenge was squandered by a bungled tyre strategy and Alonso walked away from the crash.
Rosberg's 15th career victory was also his fourth in succession after the German won the final three races of last season.
His team mate and pole-sitter Lewis Hamilton finished second, some eight seconds behind after recovering from a chaotic start that pushed the defending world champion back to sixth at the first turn.
Ferrari's Sebastian Vettel led for much of the race but his advantage was eroded by poor tyre management, especially after Alonso's crash brought out a red flag, as his compatriot Rosberg coasted home.
"Yeah! awesome, guys, awesome. Great start to the season," Rosberg yelled down the team radio.
New team, the US-backed Haas, celebrated points on debut, with Frenchman Romain Grosjean finishing sixth behind Red Bull's Daniel.
