A person has moderate injuries after an ammonia leak at a Central Hawke's Bay freezing works.

Fire and Emergency New Zealand received a report of the leak at Silver Fern Farms on Fraser Rd, in the rural community of Takapau, 20 kilometres west of Waipukurau, about 2pm on Tuesday.

A St John Ambulance spokeswoman said one patient in a moderate condition was transported by ambulance to a local medical facility.

The ammonia leak was dealt with by site engineers, according to a fire communications spokeswoman.

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Police were initially called to the incident, but ended up not attending after St John Ambulance said they were not required, according to a police spokeswoman.

A WorkSafe spokesman said they have been notified of the incident.

"We understand there may have been an ammonia leak," he said. "We are making initial inquiries to establish what our next steps might be."