ORLANDO -- Nic Hornstein was suddenly awakened by a noise - a noise that wouldn't stop.

When he looked out the window to see what was going on, he saw chaos.

"Never thought I'd see something so horrific," Hornstein said.

Hornstein was in an apartment across the street from the Pulse nightclub, the sight of the mass shooting that killed 50 people in Orlando early Sunday morning.

"I looked out the window and heard the people screaming, running from the club," he said. "Some injured, some helping the injured get away. There were some people not moving so much. Some unresponsive."

PHOTOS | Mass shooting at Orlando nightclub

Hornstein is from, and lives, in Atlanta. He was only in Orlando visiting for a bike race. But he frequently visited the area. While he never went into the Pulse club, he would pass by every so often.

"It always seemed very happy. People laughing, screaming, having a good time," he said. "But, different screams today."

As he heard the screams, he knew something was wrong. He just did not know the magnitude of it.

Thinking it was just an altercation gone wrong, Hornstein tried to rush down to help, but the swarm of police that had suddenly appeared barred him from entering the club.

"It's chilling," Hornstein said. "You read about it in the news. You always think at least it's there and not here, it will never be this close to me, and then you wake up and there it is going down across the street."

Hornstein is back in Atlanta, but he still is shell shocked by what he experienced. But as he was leaving Orlando Sunday, he saw prayer vigils and memorials begin to set up - unifying the city in mourning.

"It seems like the community is really joining together as a whole to help start healing," he said.

PHOTOS | Vigils held for Orlando victims