A “possible irritant” was sprayed or thrown Tuesday night on a "staff worker" near the Peninsula Hotel, authorities said.

Multiple ambulances were dispatched to the 700 block of North Rush Street near the Peninsula Hotel shortly before 9 p.m., the Chicago Fire Department said. Police said an unknown substance was thrown at a "staff worker" who was then transported to Northwestern Memorial Hospital for evaluation. Three other employees were treated at teh scene and released.

Fire trucks, police cars and ambulances could all be seen idling in front of the hotel with their lights flashing and sirens blaring.

Three people were in good condition and the scene was secured, fire officials said.

It was unclear what the condition of the person taken to Northwestern was.