Students from top Auckland school King's College are in a "state of disbelief" after the death of a third student since February.

A Ministry of Education trauma team has been called in to the decile-10 Otahuhu school after the death yesterday of 15-year-old Michael Treffers.

The Year 11 pupil was taken to Auckland City Hospital after an incident on the Market Rd overbridge on the Southern Motorway about 10.30pm on Sunday.

His life support system was turned off yesterday afternoon after family and close friends had visited him.

Last week, King's College students farewelled James Webster, 16, who died after binge-drinking vodka.

In February, 15-year-old William Thode died of a rare viral infection of the heart. He was found dead in his bed in his dormitory at the school.

King's College headmaster Bradley Fenner said Michael was in the same house group as William and also knew James.

"But we do not know the circumstances [of Michael's death]. We do not know what led to this, we are not aware of there being any connection or direct link."

Last night, two Facebook tribute pages set up for Michael had more than 1500 members.

Mr Fenner said a special assembly was held yesterday morning and students were offered counselling.

"It has been another very challenging day. I think the prospect of this year ... it's just a state of disbelief."

Mr Fenner said the ministry's traumatic incident team had been working with staff.

"They were assisting us in putting in place the structures and supports so students and staff get the counselling they need, and assisting us in how we manage things from here.

"Part of that is identifying the students who will be most affected by this, those who were close to the boy concerned, in his house or just his particular friends."

Students had been given a letter to take home to tell their parents about the matter.

"At that point, I had been advised by his mother that he wasn't expected to survive and we certainly wanted to let our community know exactly what was happening so they wouldn't be hearing about things via rumours," Mr Fenner said.

Earlier yesterday, the headmaster visited Michael in hospital with some of his friends from King's. "His mother really appreciated that - she specifically asked me if some of the boys could come in."

Mr Fenner said Michael did not appear to be having problems at school - he was doing well academically and was also a keen sportsman, playing waterpolo and rugby.

"He was a regular sort of a kid who was involved in a few different sports and activities. He was a good student. He was quite a popular boy."

The parent of one student said the school's response to the "hideous" tragedy could not have been better.

"They've got the trauma team, they've got internal counsellors, they've got external counsellors.

"And they've got a really strong religious programme. The reverend and the chapel are the heart of the school. They couldn't do any more. They will band together and they will get through this."

On the Facebook pages last night, photos showed Michael at the Currumbin Wildlife Sanctuary on Australia's Gold Coast, competing in running events and posing with friends.

Tony Zhang wrote, "R.I.P Michael, Kings College has lost 3 brothers in 3 months, and without a doubt you 3 will be remembered, thode and webby will show you the way up there."

Denis James McLay wrote, "RIP, waterpolo wont be the same," and Sammy Leigh Collins wrote, "I was only just talking to you last night. Miss you so much x."

Psychotherapist Blair Schulze, who works for Youthline in Ponsonby, said grieving teenagers could experience several emotions, including shock, anger and sadness.

The most important thing for them when going through the grieving process was to talk and express their emotions, which could be done in a variety of ways, including through a counsellor, parents or friends.

"I guess one of the most important things would be to normalise whatever emotions came up," Mr Schulze said.

"People get into trouble with grief when they try to not feel something - either ignore it or get into the booze to try to suppress it."

If a teenager was feeling depressed, the best thing to do was to let someone know immediately, and to realise that the feeling was often temporary.