One person was killed and several more were injured, including a firefighter, after a gas explosion and partial building collapse Wednesday in downtown Durham, North Carolina, police said.

The blast occurred about 10:27 a.m. when a contractor boring under the sidewalk hit a 2-inch gas line, said Durham police spokesman Wil Glenn.

Fifteen people were transported to area hospitals, and the firefighter suffered serious injuries, he said.

A witness described a scene like a war zone, with first responders scrambling to ferry injured people to safety after the blast.

A witness from a building across the street said, "Half the block is destroyed." CNN has blurred a figure at center left due to a graphic injury.

"Half the block is destroyed," Jim Rogalski told CNN via text message. "Lots of injuries. Our office across the street was blown out. It was terrifying. Glass and debris everywhere. No one killed in our office but several injuries -- deep cuts, head lacerations."

Authorities are asking people to avoid the Brightleaf Square area as a fire is still active and an explosion has occurred.

"The ceiling tiles and structures collapse(d)," said Rogalski, whose workplace is across the street from where the blast occurred. "Windows blown out a block away. Our office was filled with glass, dust and debris."

A human resources employee told Rogalski and his co-workers that authorities were investigating a gas leak across the street and they should remain inside. About 15 minutes later, they heard what sounded like a bomb, he told CNN.

"The first second was stunned silence, then lots of scream(ing) in the building. Several of us shouted, 'Is anyone hurt?' " he recalled. "The injured were quickly taken to an exit."

Another person who works nearby said firefighters entered his building and told employees that workers had hit a gas line, and "we heard the big explosion right after they told they may evacuate us."

The blast shook the structure and blew out its windows, said the witness, who declined to give his name.

"It sounded like the building was going to collapse, and we left immediately," he said. Read more at CNN