At least 22 people were shot -- two who were killed instantly -- early Sunday when three assailants unleashed a barrage of gunfire on a crowd standing outside a birthday party concert at a rented banquet hall in suburban Miami, police said.

The shooters, armed with high-powered rifles and handguns, arrived and fled in an SUV that police were still searching for Sunday evening. The gunmen waited outside the party for about 40 minutes before opening fire just as revelers were leaving the celebration, Miami-Dade Police Director Alfredo "Freddy" Ramirez told ABC News on Sunday afternoon.

About 100 shell casings were collected at the scene by investigators, Ramirez said, adding that some party-goers under attack returned fire.