Students are "in shock" over a maths exam that has stumped even some of their teachers.

This year's Level 2 maths exam for the National Certificate of Educational Achievement (NCEA) was so tough that two Southland students have set up a Facebook event to "get all Level 2 maths students to storm NZQA headquarters" - the head office of the NZ Qualifications Authority, which set the exam.

An Auckland student who was aiming for "excellence" based on her past work said none of the generic questions that have been asked in the past few years were asked this year, and instead students were hit with questions that they hadn't prepared for.

"You just looked around and you could see people's faces, they were red," she said.

"There was the odd one that I could do, but I would normally want to do every question in the paper, but there were ones that I couldn't even start.

"Walking out afterwards everyone was just shocked."

She said the calculus part of the three-part exam, which also included algebra and probability, was "just insane".

A student at another school said the majority of the students were unable to complete the paper - some were in tears and left after 45 minutes because they could not answer the questions.

"The students are now asking why. Why was this the hardest paper out of all the years gone by? Why did they not keep the same level of difficulty throughout all the years?" she asked.

Teachers themselves reported problems answering some of the questions in a private Facebook group called NZ Maths Teachers.

"We can't see how this works - we tried drawing it and one of the roots is 0 so how can a tangent to the curve go through the origin. Any hints anyone? Am I missing something obvious?" one teacher asked in a screenshot forwarded to the Herald.

Another teacher posted: "I think it has some exceptionally hard questions. I haven't finished working through it yet, but I imagine a lot of our students who were confident with the last four years' past papers will have struggled."

A third wrote: "Had excellent students leave saying they couldn't feel confident they did well."

A teacher told the Herald that excellent students would probably still pass, but their self-confidence would be affected.

"It can start that downward spiral, that disheartening feeling, and their ability to sit maths papers next year can be affected," she said. "It's sad for the kids."

NZQA deputy chief executive Kristine Kilkelly said the agency had received three complaints about the exam out of only five complaints across 59 exams so far.

But she said initial feedback from the marking panel was that "students were able to respond to the questions, but students may have felt the questions were more difficult at the Excellence level".

"NZQA's marking processes are designed to make adjustments and ensure results are comparable from year to year. This includes taking into consideration any variation in difficulty from one year to the next to ensure students are not disadvantaged," she said.

She said NZQA had not asked its examiners to stop using generic questions that had been repeated in previous years.

"Questions will always vary from year to year, but they are consistent with the standard," she said.

However she said NZQA identified an error in the design of question 2d of the algebra paper (standard 91261).

"This would not have prevented students from attempting the question," she said.

"To identify the error, students would have had to complete working which markers will be able to consider. Those workings will have demonstrated excellence to the markers, so we do not expect any students will be disadvantaged.

"NZQA will review its quality assurance procedures to find any improvements for this kind of question."