Demolition crews are hard at work Wednesday morning at the scene of a building collapse in East Harlem, and it could affect subway riders all morning.

The collapse happened Tuesday while construction workers were inside. Floor after floor of the building came crashing to the ground, as the building literally split in half.

Demolition crews won't stop until the building is gone. A large crane has been working to dismantle the building at 1861 Lexington Ave. near 115th Street.

Hour after hour, floor after floor, chunk by chunk, the building will be taken apart until it is nothing but rubble.

Around 80 percent of the building already has been knocked down.

It was an amazing scene on Tuesday, as the building caved in.

Witnesses said there was a crackling sound and then the center section of the building was swallowed up -- the top floor pancaking into the basement, slicing it in half.

"We heard this crashing noise one after the other, and people were screaming and shocked," said Jose Ortiz, who was walking by the building when it fell. "Right after that, smoke filled the whole perimeter. Maybe five minutes later and I could have been under there, I had just walked under there."

The building was under construction, and about a dozen workers were in the basement. All made it out alive, and only one suffered an injury: a broken arm.

"I heard the noise, and I ran out," worker Gyro Makairo told CBS 2. "It was scary, very scary."

It's being called a miracle that no one on the street was hurt. Residents in the buildings next door hurried out.

Evacuee Julio Belmont told CBS 2, "I was in the shower when that thing happened. And, uh, the fireman came down and wanted me to come down naked."

Remaining sections of the badly damaged building were considered so fragile some subway service was suspended, and other trains were kept at reduced speeds to keep rumbling vibrations at a minimum.