Winston Peters is coming under pressure from the Coalition Government's support partner, the Green Party, to speak out about the United States' separating of children at its southern border from their non-documented migrant parents.

The Greens want Peters, the Deputy Prime Minister and Foreign Minister, to protest to US ambassador Scott Brown about the treatment of children.

Labour deputy leader Kelvin Davis and National leader Simon Bridges yesterday joined an international chorus of opposition to the current practice, saying it was cruel and inhumane.

The closest Peters got to criticism was saying New Zealand would not do what the US did but said he wanted to focus on what was happening in New Zealand, while he deputises for Prime Minister Jacinda Ardern on maternity leave, not other countries.

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"The mass detention of children and separation from their families as a part of immigration policy is unacceptable," said the party's human rights spokeswoman, Golriz Ghahraman.

"The Green Party is calling on the Prime Minister and Minister for Foreign Affairs and Trade to express New Zealand's opposition to this practice in the strongest possible terms to the United States ambassador," she said.

"We cannot stand by and let this happen.

"New Zealanders take huge pride in our country's record of standing up for what's right on the international stage," she said. "We must do that now, and use every avenue we can to push the United States to change their policy."

Amnesty International said this afternoon that more than 3000 New Zealanders had signed a petition urging the US Government to stop forcibly separating parents from their children at the border.

"The practice is nothing short of torture."

Coincidentally, Ghahraman will move a non-debatable motion in Parliament to mark refugee day.

Meanwhile, the Green Party is responsible for today's parliamentary Question Time being cut from 12 questions to 11.

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Under recent practice, the party has given its allocation of questions to the National Party, a contentious decision but taken apparently in the interests of holding the Government to account, but reserved the right to ask for them back at any given time.

Today the Greens told National they wanted their question - Question 8 – back but then failed to lodge one themselves.