Construction at a building in Houston took a nasty turn Friday when a large amount of scaffolding collapsed, causing "multiple injuries," a city agency said.

The incident occurred around 11 a.m. at at a luxury apartment building under construction at Crawford Street not far from Minute Maid Park, home of the Houston Astros, reported NBC's Texas affiliate NBC DFW. Footage from the scene showed firefighters picking through piles of metal on the ground that appeared to cover a large section of a city block.

Houston's Office of Emergency Management reported the injures from the collapse, saying at least four workers were trapped in the wreckage. An additional six were already rescued, with two being treated at the scene while another two were taken to the hospital with traumatic injuries, according to ABC's Arizona affiliate ABC 15. The status of the other two are unknown.

First responders arrived at the scene three minutes after the incident occurred, the Houston Fire Department reported. Within 30 minutes, more than 30 units, including several heavy rescue personnel, were already on-site, according to CNN.

Authorities have urged the public to stay clear of the area so emergency vehicles can move around freely.

It's still not clear what caused the collapse.