A recreational 4WD trip up a Canterbury riverbed on Queen's Birthday weekend that ended with a 7-year-old boy being killed is still under investigation, police say.

It comes as new details emerge of the June 5 tragedy that ended the life of "little ninja" Jurael Tutere Paul Jeffrey Bennett.

Jurael, from Christchurch, was travelling with his mother, New Zealand representative kickboxer Tash Tuuta in a 4WD vehicle being driven by her partner Ryan McCarthy.

They were coming to the end of a recreational day trip down the Waipara Riverbed – a popular off-road track – when the vehicle flipped on to its roof into the river off Double Corner Rd, near Amberley, 50km north of Christchurch.

It was around 5.30pm, nearing dark, with higher than normal water levels.

Police have named the 7-year-old boy who was killed in a crash in Canterbury. Photo / George Heard

The Herald understands that horrified friends inside another vehicle, who were part of the trip and following behind, phoned emergency services at 5.35pm when McCarthy's vehicle rolled into the river.

The Canterbury Westpac Rescue Helicopter was scrambled and needed night-vision goggles to find the crash scene in the dark, with no street lighting or nearby properties.

Police officers, firefighters, and St John Ambulance crew were already at the river when they landed nearby.

Jurael Bennett, 7, died at the scene of the accident. Photo / Givealittle

Jurael, who had been in the back seat of the rolled vehicle, had already been freed from the crashed 4WD by the friends and dragged to the riverbank.

After 40 minutes, resuscitation efforts were stopped as there were no signs of life. He was pronounced dead at the scene.

Today, a police spokeswoman confirmed inquiries into the crash are ongoing.

"We are continuing to work with family members of everyone involved as we continue to investigate what happened," she said.

The morning after the tragedy, Jurael's mother Tuuta wrote on social media of her heartbreak.

"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," she said.

"He had many heros in his life. He is the most caring, brave, adventurous smart and cheeky little boy you will ever meet [sic]."

In a later post the mother added: "You saved me, I wish I could (have) saved you."

A vehicle went off the road and plunged into the Waipara River, off Double Corner Rd, in Amberley at around 5.35pm on June 5. Photo / George Heard

A Givealittle page started by the kickboxing gym Tuuta belongs to has since raised more than $11,000.

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 District 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," she said.

"This is a real tragedy, it's difficult to find the right words to express but my thoughts are with them all."

Jurael's death will be referred to the coroner.