Emergency services were called to Rumwood Green Farm in Langley at around 2pm on Wednesday following a suspected chemical leak.
Paramedics treated 57 people, believed to be staff at the plant, for carbon monoxide exposure.
More than 40 firefighters, an air ambulance and a specialist chemical unit were called to the scene on Sutton Road.
A chemical tent was set up at Maidstone Hospital, in preparation for the arrival of patients.
One person was taken to Pembury Hospital in Tunbridge Wells.
The emergency services are likely to remain at the scene throughout the night to determine what caused the incident.