Passengers on a Jetstar flight last week were "disgusted" when a family changed their child's soiled pants on one of the aisle seats.

One passenger, who did not wish to be named, said he was on flight JQ284 from Dunedin to Auckland last Friday seated near a family with a young child he estimated to be aged around 4 or 5 years old.

"This kid shat [sic] himself, so they got him naked and started to change him across from us," he said.

A flight attendant told the parents they couldn't change the child on the seat, he said, but they "completely ignored that".

"The attendant told them there was a changing table in the bathroom, they definitely could have used that," he said.

"Later on in the flight, the kid needed to go again so the grandma who was travelling with him and his parents got out a bottle and got him to piss in the bottle.

"They gave the bottle back to the grandma who wiped it off with tissues and stuffed the tissues in the seat in front of her."

The other passengers were all looking around wondering what was going on, he said.

"The guy in front of us thought it was pretty disgusting too. A few people made comments to them, but most people were too uncomfortable to say anything."

He didn't blame the child, he said, but thought his parents should have taken him away from the other passengers to change him.

"It was pretty rough for the passengers, the whole cabin smelt like a toilet. I'm definitely not going to be flying Jetstar again," he said.

His girlfriend, who was on the flight with him, had complained to the airline and had been told there was nothing Jetstar could do to compensate.

"I explained what had happened and the guy I spoke to said, 'sorry to hear that, I'll pass it on to management'," she said.

"He refused to refund us our flights, he said they don't refund for things like that. I'm not sure what the next step is but we definitely want to take this further."

A Jetstar spokesman said the airline was sorry to hear customers had been unhappy with their onboard experience.

"For hygiene reasons and the comfort of all our customers we encourage families travelling with infants and young children to use the change table facilities in our toilets on board our A320 aircraft to change nappies," he said in a statement.

"Rubbish bins are provided in the toilets on all our aircraft for the disposal of soiled nappies."