Injured firefighters responded in response.
A Dallas apartment building collapsed shortly after firefighters were called in to investigate emissions of carbon monoxide, according to authorities.
When firefighters arrived at the South Dallas headquarters around 10:30 am local time, they noticed the smell of the air surrounding the building, according to Dallas Fire-Rescue.
The explosion occurred while firefighters were investigating the incident, causing the two-story building to collapse slightly, officials said.
The blaze was erupting at 11am, Dallas Fire-Rescue spokesman Jason Evans told reporters at a news conference Wednesday afternoon. About half the building appeared to be badly damaged and a pile of debris from the building appeared to be surrounded around the building.
“The damage is huge,” Evans said. “The drop is full.”
Seven people, including four firefighters, were injured in the blast and taken to local hospitals. Two victims were in critical condition; five are in stable condition, according to the Dallas Fire-Rescue.
Residents began talking about the air on Tuesday morning, Evans said. He did not elaborate on the initial investigation into those reports.
It was unclear what caused the blast, fire officials said. More information was not available there.
ABC News’ James Scholz contributed to this report.