All 23 people taken to a hospital in the Niagara region after an acid spill at an auto plant have been discharged.

That includes three who were directly exposed to a vapour cloud of hydrochloric acid.

The spill happened at the THK Rhythm Automotive plant in St. Catharines Tuesday morning.

Emergency crews were called to the business after staff accidentally hit a valve, which released about five litres of the hazardous chemical.

WATCH: Over 20 people sent to hospital after chemical spill at St. Catharines facility

Fire Chief Dave Upper says three people were directly exposed through skin contact and inhalation.

The liquid transformed into a vapour cloud and 20 other staff members in the large space were exposed solely through skin contact with the vapour.

Affected staff used a decontamination shower on site before going to the hospital.

The hydrochloric acid was contained within the plant and there was no risk to public health.