Prime Minister John Key says the treatment of a French au pair jailed overnight and deported after travelling to Queenstown with an Australian family on holiday was "heavy-handed".

The 18-year-old au pair, Manon Pache, was in New Zealand in December for a week visit with the family she worked for in Australia. Her employer, Pip Johnston, who has complained to Immigration NZ, says she was holidaying with them and was not being paid or expected to work.

After Ms Pache told immigration officials it was possible she would babysit the children on occasions she was put in a police cell overnight and deported back to Australia the next day.

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Au pair on week's holiday locked up and deported


Mr Key said he did not know the full details but did not believe it was appropriate.

"There were two parts to it and it seemed pretty heavy-handed to me.

"It might be technically what they could have done but I think there are other options as to how they could have handled the situation."

Asked if she should have been allowed to say, he said it was possible there was an explanation.

"It sounds pretty harsh to be deporting someone because they're babysitting when they're an au pair."