A teenager swept out to sea at Waihī Beach was part of a Hamilton school group on an excursion to the coast.
The boy was reportedly caught in a rip on Friday afternoon, with one of his teachers making a "heroic" effort to rescue him.
Waihi Beach was not patrolled by lifeguards at the time, a Surf Life Saving spokeswoman said.
Melville High School confirmed one of its students was involved in a serious incident and now missing, with the search for the student now entering its third day.
"It is with much sadness that we share with you that there has been a serious incident at Waihī Beach this Friday afternoon and one of our students is missing," the school said on its Facebook page.
"The school is supporting the family, students and staff as we work through the challenges of this event."
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Police received a call about the boy getting into trouble near the Top 10 Holiday Park on Beach Rd at about at about 12.40pm on Friday.
He had been part of a group swimming in the area. Residents understood he was a boy of about 17.
Search efforts have been underway since Friday afternoon.
"Today's search will once again be assisted by Waihī Beach Lifeguards using inflatable rescue boats and jet skis," police said.
A parent at Melville High School, who did not want to be named, said her son's friends were present when the drama took place and said the missing student had been part of a geography class outing.
"They had done their class work and were all having a swim before heading back to Hamilton," she told the Herald.
"The young lad got caught by a rip. A teacher tried desperately to save him."
She said the incident had really affected students.
"I don't think we ever expect to send our children on a school trip and they never come back," she said.
Parents and friends of the Melville school community shared their prayers and support underneath the school's Facebook post.
"The loss of one of our own cuts oh so deep," wrote one poster.
"Our thoughts, prayers and love go out to the whanau effected (sic)," another said.
"I refuse to believe your (sic) not with us," one poster said in addressing the missing student.
Surf Life Saving has had an inflatable rescue boat and jetski searching the area at intervals today.
The next sweep by the vessels was due to take place at 4pm. Conditions in the water had improved making it easier to search close to the coast, a spokeswoman said.
The spokeswoman said Waihi Beach was not patrolled at the teen was swept out to sea.
The beach is patrolled daily during the peak summer season, but not that had passed it was only patrolled on weekends, she said.
One the alert was raised on Friday, Surf Life Saving scrambled its Waihi and Whangamata emergency call out squads to join the search.r
A Waihī Beach Surf Lifesaving Club representative said on Friday that lifeguards were in the water and "giving it their best effort".
Two Coastguard vessels had taken part in the search, along with the Auckland Westpac Rescue Helicopter, which carried out grid searches in the area, she said.
Police described Friday's sea conditions as rough and two local residents told the Bay of Plenty Times surf conditions were "quite gnarly".
The past three days have been a horror period in the water after four people drowned at Langs Beach and Baylys Beach in Northland, and the Police Dive Squad located a body from the Whanganui River yesterday.
This included a young boy's death yesterday after being snatched by a wave as he played in the surf at Napier.
In that incident witnesses described the heroic efforts of two young police officers, who risked their lives in a desperate bid to reach the child.
The 9-year-old died at the scene after police received a report of a person struggling in the water off Marine Parade about 3.42pm.
It is understood he was among a group who were swept out to sea from the water's edge.
Water Safety New Zealand chief executive Jonty Mills said there had been 20 water fatalities this year, compared with 22 at the same time last year. The deaths were across a range of ages, activities and environments.
"Any waterway presents a hazard," he said.