Prime Minister Jacinda Ardern will give an update about the "hugely concerning" impact of the volcanic eruption on Tonga at 3pm on Sunday.
"Till then, I know we are thinking of our pacific friends and family," Ardern said on her Facebook page.
"The images of the volcanic eruption in close proximity to Tonga are hugely concerning.
"Communication as a result of the eruption has been difficult, but our defence force team and Ministry of Foreign Affairs are working as we speak to establish what’s needed and how we can help.
"I’ll be giving an update again at 3pm. Till then, I know we are thinking of our pacific friends and family."
MPs across parliament are among the many who have shared their aroha and concern for those affected.
Minister for Pacific Peoples Aupito William Sio urged worried families to remain calm on Saturday night as communication difficulties emerged.
"To our Tongan families in Aotearoa, please don't panic if your families in Tonga aren't responding to your phone calls. Stay calm, it is too early to assess and for you to worry too soon. It maybe that the communication systems are down or overloaded, Minister Sio said on Facebook.
"We all know that none of us can bend the will of Mother Nature. We must be patient. We are a resilient people, that pray and hope for all good things in times of crisis.
"Stay tuned to your local radio stations for regularl reporting - so stay tuned, and support your vulnerable families to cope during this time."
Labour MP Jenny Salesa, who is Tongan, said the situation is "heartbreaking".
"Praying for all of our beloved people in the Friendly Islands of Tonga, Salesa said on Twitter.
"The satellite image of the volcano eruption as well as videos recordings of the tsunami has been really heartbreaking to watch. Most of Tonga’s quite flat so tsunamis can be devastating! ‘Ofa atu Tonga ‘Eiki."
Government minister Carmel Sepuloni added that "We’re thinking of everyone at the moment".
"My thoughts and prayers to all our people and families in Tonga. We’re thinking of everyone at the moment. ‘Ofa lahi atu to the Kingdom of Tonga," Sepuloni said on Twitter.
Green Party co-leader Marama Davidson said she was sending "so much love to Tongan families and people experiencing some terrifying moments right now".
"Went to bed last night and woke up thinking of Tonga and all our Pacific nations with the eruption of the Hunga-Tonga-Hunga-Ha'apai underwater volcano yesterday, Davidson said on Facebook.
"Sending so much love to Tongan families and people experiencing some terrifying moments right now. Thinking of Tongan communities here in Aotearoa and around the world. Thinking of all my precious friends who whakapapa to Tonga and other islands at risk right now. And I extend that aroha to our own potentially threatened east coast communities, my own people and homelands.
"Grateful and hopeful for any support our country affords to our Pacific neighbours and how else we can help if needed. Ofa atu."
Māori Party leaders Rawiri Waititi and Debbie Ngarewa-Packer both said their "thoughts and prayers are with our whanaunga in Tonga".
Late Saturday evening, Waititi posted "Ko ngā whakaaro nui kai o tātau whanaunga o Tonga Tapu. Our thoughts and prayers are with our whanaunga in Tonga. May the power of god give you all the strength and power to get through these trying times. Be strong, loto lahi. Mālō ‘aupito!"
In her Facebook post, Ngarewa-Packer added "#Tonga thinking of all the whānau, elderly, vulnerable and tamariki, praying for your safety. Be strong, loto lahi, Mālō ‘aupito."
National's Dr Shane Reti was another to share his feelings of concern.
"Our concerns and sympathies are with Tonga and the people of the Pacific just now.
"I have reached out to the local Northland Pacifica Leaders, the Tongan consulate and the Minister for Pacific peoples to see how we can help," Dr Reti said on Facebook earlier today.