WorkSafe is investigating Fonterra's Edendale dairy factory after two emergencies there within a month.
A 15m-high milk silo collapsed at the Southland plant last Friday, rupturing pipes and shutting down part of the factory.
A month earlier, 5000 litres of nitric acid and caustic soda, which were used there as cleaning chemicals, spilled from storage tanks.
The government's health and safety regulator said its staff had visited the Edendale site about the spill, and were in contact with the company again now about the silo collapse.
WorkSafe said Fonterra was fully cooperating with its investigations.
Southland District Council, which holds the building consents for the Fonterra factory, said it had no reason to question the plant's maintenance record.
Edendale is Fonterra's largest operations site, with 600 people employed at the site.
Fonterra's website said the plant had been in operating for over 133 years, making it New Zealand's oldest manufacturing site.
It processes more than 15 million litres of milk per day, about 650 tanker loads.