A person has been in contact with a potentially deadly substance and had to be decontaminated outside Tauranga Hospital today.

The Fire Service's decontamination unit responded this afternoon to an incident where it is understood that someone had been contaminated with paraquat, a highly toxic weed killer, fire north communications shift commander Steve Smith said.

Only one person had been contaminated but it was unclear how they came into contact with the potentially-deadly substance, Smith said.

"I don't know if someone came into the hospital suffering the effects of paraquat...or if someone at the hospital came into contact with it," Smith said.

"We used to use it for killing weeds," he said, adding it was "very, very deadly".

The person had gone through a decontamination unit that the Fire Service had set up on the hospital site.

The decontamination process involved the person taking off their clothes, being hosed down, entering a pool and then possibly going through the process again, Smith said.

All material contained through the process would then be disposed of at a hazardous substances site.

One fire truck was still at the hospital but the decontamination process was now complete.

The person's condition was unclear as Tauranga Hospital could not be reached for comment.

Breathing in paraquat could cause lung damage and lead to a disease called paraquat lung, information on the United State's government's National Library of Medicine's website states.

It is particularly harmful if it touches the lining of the mouth, stomach, or intestines and could also damage the kidneys, liver, and esophagus.

It could be deadly when swallowed.

- © Fairfax NZ News