Labour leader Chris Hipkins is calling for an urgent ceasefire in Gaza, saying "the violence and the killing has to stop".
Speaking on Sunday as party leader and not caretaker Prime Minister, Hipkins called for a halt to the "appalling attacks and violence".
He said he is "particularly concerned" the actions of Israel's defence forces are "disproportionate and indiscriminate".
Israel has vowed to annihilate the Hamas militant group that controls Gaza after its fighters killed 1200 people and took 240 hostages in an attack in October.
In response, Israel launched a major bombing campaign followed by a ground operation. Gaza authorities say more than 12,000 people are confirmed dead.
New Zealand's response to the conflict is under scrutiny, with one survey suggesting 60 percent of Kiwis agree the New Zealand Government should call for an immediate ceasefire in Gaza.
Hipkins said he is "appalled by the devastation and loss of life".
"I, and the Labour Party, cannot stand by any longer in the face of the horrific scenes we are witnessing without calling for a ceasefire," Hipkins said.
"We are urgently calling for a ceasefire. Israel and Hamas need to immediately ensure the conditions for a ceasefire are met and to commit to a lasting peace in the region."
He acknowledged Israel had a right to defend itself, however warned "that right is not unlimited".
"All parties need to act in accordance with international law and protect civilians," he said. "While we recognise the right to self-defence, we are particularly concerned that the actions of the Israeli Defence Force are disproportionate and indiscriminate."
"We also urge Hamas to release all hostages immediately and without condition and to be part of the process to work towards peace."
He also expressed deep concern for the humanitarian consequences of the conflict and the blockade hindering essential services in Gaza.
"We are calling on Israel to allow movement of supplies and all parties to support the departure of those who choose to leave," he said.
"Ultimately, we want to see a just and lasting peace that recognises the existence and self-determination of Israelis and Palestinians. We encourage the parties to work to a two-state solution within secure and recognised borders where all citizens enjoy equal rights and freedoms."