Dozens of people are dead after a school shooting in Newtown, Connecticut, Friday morning.

Sources say at least 20 of those killed at Sandy Hook Elementary School were children.  

The initial calls came into police around 9:40 a.m. ET. One parent inside the school told CNN that she heard what sounded like at least 100 rounds being fired.  Authorities quickly moved students to a nearby firehouse, where parents frantically sought information about their children.

In an HLN interview Friday morning, Dr. Drew said, “Imagine being one of the parents in the fire station. They know the school has been evacuated and their kid hasn't shown up. There cannot be a worse feeling in the world.”

He added, “We spent a lot of time trying to figure out what the [gunman in Oregon] did -- how it could have happened. That was clearly a kid who, for whatever reason, was not in reality in that moment. But this [school shooting] is something far, far more sinister. This is really one of the worst things that I have been associated with. I don't care what the details are. This is the stuff of evil. This is really bad.”

According to police and a parent who witnessed the incident, the school’s principal and a school psychologist were also killed.

The shooter is dead, but it’s unclear whether police took down the gunman. The FBI and ATF are now assisting with the investigation.

The elementary school is about 60 miles north of New York.

Tonight, Dr. Drew and his guests will have full coverage of the story and explain what people can do to help cope with such a tragic event -- at a special time, 9:30 p.m. - 11 p.m. ET on HLN.