Wichita ? An apparent natural gas explosion Wednesday morning knocked down a wall on two floors of the Marshall Middle School, which was not in session because of the Thanksgiving holiday.

“We can thank the Lord this occurred today and not yesterday,” Wichita Deputy Fire Chief Mike Rudd told reporters.

Two construction workers were taken to Via Christi Regional Medical Center-St. Francis for treatment. One with minor injuries was released. The other was admitted with serious injuries that were not considered life-threatening.

The explosion heavily damaged a new addition that was nearly done.

About 100 students and 10 teachers would have been in the building had the section been in use, Supt. Winston Brooks told The Wichita Eagle.

The explosion knocked debris into the street and hit houses across the street. The concussion from the blast also damaged windows and doors of nearby homes, Rudd said.

About 25 residents near the school were evacuated and taken to a church for shelter, Rudd said. A number of construction workers and school personnel were in the building at the time of the blast.

No one was trapped inside, he said.

Wichita firefighters monitor the scene of an explosion at Marshall Middle School, in a part of the building that was under construction. School was not in session Wednesday because of the Thanksgiving holiday. Two construction workers were injured in the explosion, which is under investigation.

Kenton Cox, manager for the project, said the classrooms and science labs in the damaged section would have to be torn down and rebuilt — at least six to eight months of work.

“I’ve never seen anything like this in my career,” Cox said.

Heidi Baxter, who works for computer services for the district, was inside the building when the explosion occurred.

“I felt it. The floor shook and the ceiling tiles were coming down,” she told The Eagle. “I didn’t realize what had happened until I came outside. It was a big surprise to see how damaged it was.”