Around 500 to 600 teenagers occupied the Discovery Green area of downtown Houston in what is known as a "teen takeover," according to HPD.
As police began clearing the crowd, a large group began gathering nearby. Houston Police continued their goal of clearing the area when gunshots were fired, HPD said.
More officers arrived on scene to assist, and more gunshots rang out, HPD said.
Houston police said it took them over three hours to clear the scene.
One minor and one adult were detained, according to HPD Captain Jonathan French.
"Both were found to be in possession of firearms. Both were found to be in that area where we had shots fired. Right now, we have an investigation division that's helping us sort that out. Those two will probably be going downtown for further investigation and that's still ongoing at this moment," French said.
There were no reported injuries, according to HPD.