A fun family outing to the beach has ended in heartbreak after a sand dune collapsed on a 28-year-old father in front of his partner and children.

Kane Watson, a father of four, was playing with his three stepsons and 18-month-old daughter at Muriwai Beach on Saturday, around a 40-minute drive northwest of Auckland, when tragedy struck.

According to the Auckland Rescue Helicopter Trust, Mr Watson had been digging in a sand dune when it gave way, burying him completely.

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Emergency services responded swiftly, and Mr Watson was airlifted to Auckland City Hospital in critical condition.

Despite the efforts of rescue teams and medical staff, he succumbed to his injuries on Saturday evening.

“In seconds, laughter turned to panic as his family witnessed the unimaginable unfold before their eyes,” wrote family friend Kristalle Tayler, who set up a Givealittle fundraiser to support the grieving family.

Ms Tayler described Mr Watson as a “much-loved son, brother, partner and, above all, a devoted father.” She said the accident has left his family “shattered.”

“His greatest joy was being with his children — not only his own, but also the kids he cared for and loved as if they were his own,” she added. “To have witnessed such a tragedy and now face life without him is almost unbearable.”

In a heartbreaking detail shared on the fundraising page, Ms Tayler revealed that Mr Watson was expecting another child, due early next year.

“Most heartbreakingly, his youngest child, due early next year, will never get to meet him, but will grow up hearing stories of the incredible man who loved them before they were born.”

Police have confirmed they are carrying out enquiries on behalf of the coroner.

As of Monday, the fundraiser had raised nearly $NZD11,000 ($10,000) from 291 donations, which will help cover funeral expenses.