Disciplinary authorities in Central China's Henan province are looking into possible fraud in grading students' answer sheets in the national college entrance examination, or gaokao.

Authorities are investigating an alleged switch of four students' answer sheets and will publish their findings as soon as possible, the province's education department said in a statement on Monday.

The statement came after the parents of four students in four cities told disciplinary authorities that they suspected misconduct by the local higher education admissions office in switching their children's gaokao answer sheets.

The parents said they became suspicious after their children received half the scores they expected after doing well in mock exams, according to a WeChat post published by Su Hong, of Zhoukou, Henan, the father of one of the students.

Su accused officials at the admission office of abusing their power and colluding with others, and said the parents had handed over evidence they gathered through various means to the disciplinary authorities.

Su told the Beijing News that he took pictures of his daughter's answer sheet for the Chinese-language exam at the admission office on June 26. After seeing the pictures, the daughter said the essay was not hers.

Lu Xiaomei, the mother of a student from Shangqiu, told the newspaper the identification numbers of her daughter's answer sheets are different for the four subjects.

There were also correction marks in the answer sheets that students said were not in their handwriting.

The local higher education admission office said on Tuesday that it has repeatedly checked the answer sheets of the four students after receiving reports from their parents and found nothing abnormal.

Under China's intensely competitive and stressful gaokao, the central authorities set quotas on how many applicants universities should admit from each area, so students from provinces with larger populations will have a harder time gaining admittance to universities.

About 984,000 students in Henan took the gaokao this year, the highest number among all provinces, municipalities and autonomous regions.

Chu Zhaohui, a senior researcher at the National Institute of Education Sciences, said that instead of being organized by education authorities, the gaokao should be run by professional examination organizations to prevent possible power abuse by officials.

The gaokao is considered the most important exam for Chinese secondary students, as their scores largely determine their future. Candidates must perform well in the exam to gain admission to the best universities, where graduation guarantees a bright future with status, wealth and possible influence.