Video from the scene showed piles of metal lying on the ground outside a roughly seven-story building. The collapsed scaffolding appeared to cover a large section of a city block.
Senior Capt. Ruy Lozano, from the Houston Fire Department, told reporters that all the injured were workers at the scene -- not passersby or first responders. He described all the construction workers injuries as not life-threatening.
Firefighters could be seen walking around the scene, in some cases getting underneath the rubble of scaffolding.
As to whether there might be more hurt or even any killed, Lozano said, "We don't have any confirmation of missing workers."
Houston's Office of Emergency Management reported the collapse happened near the corner of Crawford and Preston streets -- an area not far from Minute Maid Park, the home of Major League Baseball's Houston Astros.
People were urged to steer clear of the area so emergency vehicles could get in and out.
Authorities aren't worried about so much about whether the building falling down so much as more scaffolding, Lozano said.
"There's always the potential for a secondary collapse," the senior captain said. "It's dangerous, so we're keeping people out of the way."
The Houston Fire Department reported that the first crews arrived within three minutes after the collapse was reported around 11:10 a.m. (12:10 p.m. ET). Within about 30 minutes, more than 30 units -- including several heavy rescue personnel -- were already on-site.
Lozano said one of the biggest concerns was the safety of at least 100 firefighters at the scene.
"Right now, it looks like more (like) the scaffolding is the real danger," he said.