BALTIMORE (WJZ) — Reports of an explosion at a busy downtown courthouse shuts down several city blocks. Hazmat crews and the bomb squad were brought in to investigate.

Kai Jackson explains authorities still don’t know what caused the big boom.

The source of the loud sound is still under investigation. But the reaction it caused was clear.

A booming sound rocked the inside and outside of the Mitchell Courthouse on Thursday. Authorities weren’t sure what caused it, but as a precaution, hundreds of employees and jurors were evacuated.

“I heard a noise. I heard one big noise and they said, ‘Yeah, it’s something happening outside,'” said Joe Lewton, evacuee. “And then a half an hour later, the next thing you know they’re like, ‘Alright let’s go. Pack ’em up.”

The response was swift and included the Baltimore City Police bomb squad and the city fire department. The Baltimore City Sheriff’s Office, which is responsible for courthouse security, also investigated.

“Around 2:30 today there was a large sound, a very loud sound that emanated from one of the trash cans that was outside the west building courthouse,” said Lt. Carla Lightsey, Baltimore City Sheriff’s Office.

The Department of Homeland Security was also on the scene.

Investigators didn’t find anything incendiary. They couldn’t confirm there had even been an explosion.

Authorities still haven’t determined what that loud sound was, but say through their investigation they believe something was indeed placed inside the trash can.

“In terms of casualties, we were very blessed. There was nothing there,” Lightsey said.

No one was hurt and no damage was reported. A city police bomb robot swept the area, but found nothing.

All roads closed around the courthouse were eventually reopened.