The Louisville Metropolitan Police Department in Kentucky said Monday morning that there are “multiple casualties” in the downtown area as officers are responding to  “reports of an active aggressor.”

“We are confirming reports of an active aggressor in the 300 block of East Main (Street). Please stay out of the area,” police wrote in a Twitter post. “There are multiple casualties.”

Other details about the incident, including a description of the assailant, were not provided. It’s not clear if the “active aggressor” used a gun or another weapon.

The FBI’s Louisville office wrote on Twitter that “special agents have responded to the scene of this morning’s shooting in downtown Louisville and are assisting our law enforcement partners.” Other officials called on residents to stay away from the downtown area.

Louisville Mayor Craig Greenberg also stated there was an “active police situation downtown,” telling the public to “please avoid the area around Slugger Field until further notice.”

Officials told local media that a shooting occurred at the Old National Bank building in downtown Louisville. Witnesses told WHAS-TV that they heard gunfire inside the building, while officers were heard yelling, “Active shooter at the bank.”

Kentucky Gov. Andy Beshear, a Democrat, wrote on Twitter that he was heading to the scene. “Please pray for all of the families impacted and for the city of Louisville,” Beshear wrote.

Video footage shows a massive police presence around the downtown area, while agents from the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) also were seen respsonding.

More details about the incident were not immediately available.

This is a developing story. Please check back for more updates.