Roads are open again in Motueka after emergency services were called to a chemical spill in the centre of the township.
Police said hydrogen cynamide - known as Hi-Cane - had leaked from a barrel on the back of a truck and onto the road in Tudor Street, which runs off High Street.
Cordons were placed in the area, and people exposed to the chemical were placed in decontamination showers as a precaution.
The chemical is used in the agriculture industry, but contact can cause vomiting, headaches and respiratory irritation.
Nelson resident Alison Hossain and her husband were crossing the road along with their 10-month old baby Barney in a pushchair when they passed through the liquid.
"This guy suddenly runs over and says 'no, don't walk through that' but it was too late."
Fire and police personnel quickly arrived to block the road, Mrs Hossain said.
They were put through the decontamination showers, which were set up in a tent on the roadside.
Mrs Hossain said they were required to shower fully clothed, and then remove their clothing for a further shower while their clothes were taken from them.
They were then issued with blankets and white boiler suits, which they had to wear home.
"We're heading home for hot showers. It's one of those situations where you really don't want to have to stop to get petrol," Mrs Hossain said.
She said she had seen one man at the scene being checked by paramedics after getting some of the substance on his arm.