29-year-old Casey passed away after crashing his motorcycle while attempting a ramp jump at Slayground Motocross Park near Ramona, CA which is owned by X Games gold medalist Axell Hodges.

Police and fire responded around 2:45 PM and attempted life-saving measures ... but unfortunately, he was pronounced dead at the scene. The accident is now under investigation.

Lavin, MTV's "The Challenge" host, shared a touching tribute to Casey ... saying, "The world lost one of the baddest to ever do it. I’m so sorry for his wife and kids."

"@patcaseybmx will forever be remembered for the down to earth sweetheart of a guy that he was. #bmxfamily."

Dhers also shared a pic of Casey with the caption, "Descansa en paz Pat."

6-time X Games gold medalist Kyle Baldock gave a heartfelt farewell ... adding, "I can’t believe I’m writing this, today we lost an Icon! Pat thank you for blessing all of us with your kind and loving personality."

"You are the toughest person I have ever met, we have been friends since ASA days which is like 10 years ago and you always have inspired me to go harder. We all will miss you so much it doesn’t seem real."

"I love you bro and my thoughts are with your whole family and friends. Rest Easy Pat ❤️❤️"

The X Games also posted ... saying, "We are deeply saddened by Pat Casey’s passing and our thoughts and prayers go out to his wife, children, parents and siblings."

"A true legend in the action sports community, Pat will always be a member of the X Games family and an inspiration to everyone’s life he touched."

Pat had a decorated career ... going pro at just 14 years old. He was known for nailing and creating tricks that many thought were impossible.

Pat is survived by his wife, Chase, and their two children.