A doctor whose team is treating victims of Wednesday's mass shooting in Maine described the destructive nature of the bullets used in the rampage, saying that seeing their impact was "sobering."

"This was the first time that I'd actually taken care of someone with high-velocity gunshot wounds," Dr. Richard King, chief of trauma at Central Maine Medical Center, told CBS News on Friday. "I'd read about them ... but to actually see them in person and see the destructive ability of those rounds was really quite sobering."

"Most, if not all, of our patients had at least one of those really severe wounds," he said. "Absolutely destructive. Complete destruction of the surrounding tissue is really, really quite something."  

The weapon used in the Lewiston shootings, which left 18 people dead and 13 others wounded, was a semi-automatic rifle with an extended magazine and scope, CBS News senior investigative producer Pat Milton reported.

King said the hospital took about six patients with gunshot wounds to the operating room after the shootings and that most of them were still being treated as of Friday morning. King said a child was among those receiving treatment. 

The trauma surgeons have seen many gunshot wounds before, King said. But the injuries from the weapon used in Wednesday's shootings aren't what he is accustomed to seeing. 

"What you often will see is maybe a small, what we would call an entrance wound," King said. 

But "with these high-velocity rounds, you can actually see the exit wounds and they cause a massive amount of destruction, gaping holes," he said. Even more problematic is they can destroy parts of the body beyond "the bullet track," King said. 

"Often these rounds will hit bone, shatter bone, and the bone itself becomes a missile or projectile," King said. "So, lots of destruction. Absolutely devastating injuries."

The shooting started at Sparetime Recreation, a bowling alley in Lewiston, where seven people were killed; six males and one female died of apparent gunshot wounds, state police Col. William Ross said during the news conference. 

At the second shooting scene, Schemengees Bar and Grill, about 4 miles away, seven males inside the establishment and one outside were killed. Three other people died at an area hospital.

Authorities have identified the suspect as 40-year-old Robert Card, an Army reservist who remains at large and is considered armed and dangerous. A massive manhunt to find him has enlisted multiple federal agencies and spans from New York to the Canadian border.