Thirty people were being treated at the hospital Sunday night after a large hazmat team response was called to a business in Salem, Massachusetts.
The initial call came in at 3:40 p.m. Sunday for what appeared to be a chlorine leak inside Thermal Circuits at 1 Technology Drive.
Employees inside the building were evacuated while the fire department and state hazardous materials team responded.
Deputy Fire Chief Alan Dionne said the first incident lasted four hours and concluded around 8 p.m. when the building was declared safe to re-enter.
Once the scene was cleared, employees on the second shift were allowed inside.
Around 9:30 p.m., workers began complaining of nausea and vomiting, saying they weren't feeling well. Multiple workers exited the building at that time and there seemed to be an extreme panic, according to Dionne.
The Hazmat team determined that the illness that workers were experiencing was not related to the earlier chlorine leak.
Multiple patients were located upon arrival, and the Salem Fire Department set up numerous units on scene with a staging area near Salem Hospital.
Twenty patients were being treated by the Salem Hospital emergency room staff, according to a tweet from the North Shore Medical Center late Sunday night.
Salem Hospital said some patients were transported from the scene, while others were walk-ins.
An unknown number of other patients may have taken themselves to various hospitals, according to Dionne.
Multiple patients complained of burning eyes and difficulty breathing.
A regional hazmat team will go back into the building, which will not be open on Monday. OSHA will be on site.
The city of Salem said the issue is contained to the inside of the building, and there is no danger or evacuation required at nearby properties.
The Lynn Fire Department said in a tweet they are covering for the city of Salem due to the ongoing Hazmat incident.