The number of people in New Zealand who have had, or may have had Zika, has hit 100.

Those who have been infected include a girl between 1 and 4 years old, three children aged 5 to 14, and a woman who never travelled overseas whose infection has now been confirmed as stemming from sexual contact. Their identities are unknown.

One person needed hospital treatment for Guillain-Barre syndrome, a potentially serious neurological condition linked to Zika in which the immune system attacks the body.

That person is now out of hospital, but the Ministry of Health did not know the patient's current condition.

Although the Ministry said the number of cases is tracking as expected, its senior advisor for communicable diseases, Dr Ryan McLane, said it remains on alert.

"It's hard to predict the future but we will continue to watch this disease very carefully.

"We're keeping a very close eye on the virus, on its spread throughout the world, and we don't anticipate reducing that surveillance any time in the near future," he said.

McLane said many things are not clear about the virus, and the ministry will change its response as more becomes known about it.

Overseas, images related to Zika have often focused on microcephaly, the condition in which babies are born with an abnormally small head and an underdeveloped brain.