Leonidas, also known as Leo, was reported missing at 5:40pm on Tuesday after he disappeared from Ngāti Tama Park in Upper Hutt, north of Wellington.
After an extensive search involving more than 100 people from the local community and emergency services, the child was found dead in the Hutt River/Te Awa Kairangi at 9:15pm.
"This is an absolutely tragic outcome and our thoughts are with the boy’s whānau," a police spokesperson said.
"Police would like to thank all those who assisted in the search, which included many members of our community."
A fundraiser on the New Zealand crowdfunding site Givealittle is now underway, with almost $6000 raised by 217 donors at the time of writing.
Created by Leo's aunty on Wednesday, the Givealittle hopes to raise money for the five-year-old's funeral and to help get the family home.
"As some of you may know, we lost our beautiful boy Leo yesterday evening while down at the river. Thank you to everyone who came by to help in the search for our boy, but this is only the beginning of a very long journey ahead," she wrote.
"As we know funerals can be a massive strain in the whānau at an already difficult time, so anything is appreciated."
On Wednesday morning, a rāhui ceremony was held at the park, led by kaumātua Jo Huriwai of Ōrongomai Marae and attended by Upper Hutt mayor Wayne Guppy, members of the marae and the wider community, Stuff reports.
A rāhui prohibits access to an area of water or land and restricts activities, such as swimming, until it is lifted. It is a temporary ritual that separates people from tapu. It will remain in place for the stretch of river beside Ngāti Tama Park until one day after the tangihanga, the date of which has yet to be confirmed.
"Due to an incident in Upper Hutt yesterday evening there is a rāhui in place until further notice for Te Awa Kairangi/Hutt River beside Ngāti Tama Park. Please do not access this area of Te Awa Kairangi/Hutt River at this time," Hutt City Council said in a statement on Wednesday.
"A rāhui is a form of tapu, a cultural practice that restricts a range of activities, including swimming or mahinga kai/collecting food from the water out of respect for the deceased.
"Our thoughts are with the whānau, and the Upper Hutt community at this time. Arohanui and kia kaha."