The Ministry for Primary Industries says it is still not aware of any incidence of illness connected to contaminated infant formula.
Three batches of whey protein concentrate totalling 38 tonnes and used in infant formula have been found to be contaminated with the bacterium that can cause botulism.
It was produced at Fonterra processing plants in Waikato in May 2012 but only made known at the weekend, prompting product recalls and import bans in some countries.
Infant formula company Nutricia on Monday night changed its recall from a voluntary recall of limited batches of two Karicare products to a full voluntary recall.
The company said all batches of Karicare Stage 1 New Baby Infant Formula and Karicare Gold+ Stage 2 Follow On Formula are being recalled. However, it said none of the products tested and sold in New Zealand indicate any contamination.
Health Minister Tony Ryall said on Monday that people should regularly check its website for any updates on what formulas can and can't be used.
Ministry officials are working with suppliers to ensure that a back-up supply of infant formula is available if required.
Otago University microbiology lecturer Heather Brooks said on Monday that botulism is extremely rare in New Zealand, with the last case reported 28 years ago. Symptoms include sleepiness, poor feeding combined with constipation, an expressionless face, weak or hi-pitched crying and drooling.
Parents and caregivers with any health concerns should contact Plunket or the Ministry of Health's Healthline. Plunket said more than 700 phone calls have been answered by its call centre since the weekend.