BALTIMORE (WJZ) — At least 21 people were taken to area hospitals after an explosion at the Baltimore Gas & Electric building in downtown Baltimore Wednesday morning. Eyewitnesses told WJZ-TV they heard and felt a large explosion just before 8:30 a.m. Then, they saw scaffolding fall from the building in the 100 block of West Fayette Street.

Two contractors who were cleaning the building windows were left clinging to the remaining scaffolding on the Lexington Street side of the building for about 30 minutes. They were later rescued by the fire department’s special operations team, who broke a window on the 10th and 11th floor and pulled the men through.

READ MORE: Will There Be A National Vaccine Mandate?

A total of 23 people were rescued from the building; 21 were taken to area hospitals for treatment. Two people refused treatment. Of those injured, nine are critical and one is in serious condition.

The building’s roof also partially collapsed.

The good news is that most of the building was empty due to the upcoming holidays and the pandemic. Firefighters swept the building after the incident to make sure no one else was inside.

BGE said construction work was underway on the building’s air handling and boiler system and that likely caused the incident.

BGE said they do not believe the explosion was gas-related.

Here’s the full statement from BGE:

On Wednesday, Dec. 23, 2020, a construction related incident occurred at BGE’s offices at 2 Center Plaza in downtown Baltimore. Construction work was occurring on the building’s air handling and boiler system, which likely caused the incident. The incident was not natural gas related. The building’s gas service was not active due to the construction work. The Baltimore City Fire Department has confirmed there are people being treated for serious but non-life threatening injuries. The building was largely empty due to the upcoming holidays and the pandemic. Window washing scaffolding was compromised because of the incident and a window washing crew was pulled to safety by the fire department. Fire department and BGE crews are on scene.

When the explosion happened, it blew out some of the windows. An eyewitness told WJZ’s Annie Rose Ramos that he was walking in the area when he heard and felt the explosion. He said the ground shook under him and he could see smoke in the air.

“I was walking on this side of the street past the Radisson [hotel] and the glass on the building shook and it went ‘boom,'” eyewitness Roger Lewis said, “and I didn’t know what it was. And we saw debris falling across the street over there.”

The incident happened on the 16th floor, per the city firefighters’ union.

WJZ saw multiple people being brought out of the building on stretchers. Two of the injured were being treated on the ground for burn-related injuries before they were transported to an area hospital.

Roads have been closed in the area and motorists are being asked to take alternate routes.

Now crews must remove the remaining scaffolding left on the building.

Chief Niles Ford said crews will do this methodically and slowly to make sure the scaffolding is safely removed.

Baltimore Mayor Brandon Scott released a statement later Wednesday afternoon, thanking Baltimore City Fire and first-responders for their work.

It reads in full:

“This morning, an explosion at the BGE Building ignited a fire near the top of the building, trapping people on the surrounding scaffolding. The Baltimore City Fire Department remains on scene as the cause of the explosion is still under investigation.

Thanks to the swift action of our Fire Department, 23 people have been rescued, 21 of whom have been transported to area hospitals. Nine are in critical condition, one is in serious condition, and no deaths have been reported.

I want to thank BCFD and our first responders for their life-saving work today. Without their bravery and quick response, the outcome could have been much worse. As the Fire Department’s investigation continues, my office will provide updates.”

The investigation continues into the explosion. ATF Baltimore and the state’s fire marshal’s office are working with Baltimore city fire and police on the incident.

MORE NEWS: Child Tax Credit: Monday Is Deadline To Opt Out Of Advance Monthly Payments