Christchurch 7-year-old Jurael Tutere Paul Jeffrey Bennett died at the scene after a vehicle went off the road and plunged into the Waipara River, off Double Corner Rd, in Amberley about 5.35pm.
"Our thoughts are with Jurael’s whānau at this extremely difficult time," a police spokesperson said.
In a social media post, Jurael's mother Tash Tuuta said they had lost their "little ninja" on Sunday night.
"He, myself, Ryan McCarthy were in an accident and sadly Jurael didn't make it he fought to the very end but died at the scene.
"He had many heros in his life . He is the most caring ,brave, adventurous smart and cheeky little boy you will ever meet. [sic]"
A Givealittle page started by the kickboxing gym Tash belongs to had raised more than $4000 as of Monday morning.
A second Givealittle page set up by friends of the family says: "We are all broken from the news of this and want to come together for Tash during this unbearable time."
Hurunui Mayor Marie Black earlier said she was deeply saddened by the crash. She was not aware of the circumstances of the crash or those involved.
"I can only express my deep sympathies to the family at this stage, as they come to terms with a tragedy such as this.
"This is a real tragedy, it's difficult to find the right words to express but my thoughts are with them all."
The death would be referred to the coroner.
