UPDATED: July 31, 2018 4:20 PM Shortly after 4 p.m. there was another collapse inside a Las Colinas parking garage where 21 vehicles were impacted by an earlier collapse.

Assistant Fire Chief Jack Taylor says there appeared to be no injuries in the initial 11:30 a.m. Tuesday collapse in Irving, northwest of Dallas, or in the 4:30 p.m. collapse of an adjoining section.

But as a result, Irving Assistant Fire Chief J. Taylor said the garage is blocked off and police will monitor it.

IRVING (CBSDFW.COM) – At least 21 vehicles were impacted when the second story of an office parking garage collapsed in Las Colinas.

It happened at O’Connor Ridge Office Park’s parking garage on 4545 Fuller Drive.

While the official cause of the collapse is unknown, OSHA is investigating what they said appears to be “spontaneous collapse caused by volatile soil, swelling between seasons”.

According to the Irving Fire Department, a preliminary search indicated no one was hurt. A more intensive search is underway.

“There are thousands of pounds of concrete and steel affecting these vehicles,” Irving Assistant Fire Chief J. Taylor said. “Both the Irving Search and Rescue Team and Dallas’ Urban Search and Rescue Team have the capability to move very heavy debris in short fashion.”

When the 40′ by 40′ section of the second floor collapsed, nearby workers were startled by the loud bang. Footage from Chopper 11 showed structural damage and vehicles tossed like toys. Massive sheets of concrete came to rest on some cars. Other vehicles were piled against one another.

Firefighters Search Parking Garage Collapse (CBS 11)

“Our office windows look directly out over the parking deck. We heard a loud noise, saw a large dust cloud… so we ran to see if anyone needed our help. We found two women who were walking into the parking garage at the time, but they were fine,” said witness Michael Clifton. “The way that it sounded, it sounded like someone dropped a dumpster trash can from a few stories up.”

Firefighters went car-to-car searching the mangled mess for anyone who may have been inside their vehicle or the garage at the time.

“The challenge with this is, this structure itself isn’t safe for out rescuers to go inside and actually begin that effort of doing that work [searching under collapsed area]… it causes a lot of vibration,” explained Taylor.

A woman took photos showing the extent of the damage Taylor alluded to and shared them on Facebook.

Another witness told CBS 11 News that the collapse sounded like an earthquake.

“It was kind of gut-wrenching more than anything else. We were hoping we didn’t find anyone inside the cars,” added Clifton. “It was very eerie. You could smell gasoline and rubber.”

The fire department said a secondary collapse is their biggest concern right now. Additionally, engineers need to make sure the area is safe before cleanup begins. But it’s not clear exactly how long that will take.

After that, people can get their cars.

CBS 11 News has asked the City of Irving for a copy of the building’s plans and permit from 1978, but so far officials have not made that information available.

Firefighters Search Parking Garage Collapse (CBS 11)