A truck carrying a crap ton of fireworks in Ocean City accidentally detonated Sunday AM, freaking out bystanders who were in the area ... but ultimately serving as an early indicator of what was to come. Seriously, it was like a full-blown firework show right there on the sand.

Of the mishap, the Ocean City Fire Dept. says ... "There was an unintentional discharge of fireworks that were being set up on the beach for the Town’s fireworks show." They added, "During the unintentional discharge, employees of the fireworks company received minor injuries and refused transport to the hospital by Ocean City Paramedics."

Thankfully, no one was seriously hurt ... but this could have turned ugly fast. In fact, it's eerily similar to another detonation gone wrong right here in L.A. from last week -- when the LAPD's bomb squad tried safely disposing of thousands of pounds of illegal fireworks they'd confiscated ... but ended up sending shockwaves through a southside neighborhood instead.