Emergency services were called to the holiday park at about 1.20pm.
Holiday park owner Erwin Beiboer said he had not seen anything like it before.
The tornado formed for a few seconds in a group of caravans and tents, he said.
"There were people in the tents and were lifted up a few metres. Luckily the tent was open so they could actually fall out [and] jump out," Mr Beiboer said.
"The tent went up a few hundred metres ... over our trees into the neighbour’s paddock."
Emergency services were at the scene checking "mainly frightened" people, he said.
The campground was booked out with holidaymakers.
A Hato Hone St John spokesperson said one ambulance had been sent to the incident and initial indications had been of minor injuries.
"Four patients were assessed and treated at the scene, all in minor conditions, no transport required," they said.
A Fire and Emergency New Zealand spokeswoman said two fire engines had been sent to assist ambulance staff.
