Seven students were found to have used high-tech devices to cheat in the national college entrance exam held Monday and Tuesday in northwest China's Gansu Province, local authorities said Wednesday.

The exam papers of the students scored zero marks and police detained three people who allegedly sold the devices to the students, said a spokesman with the education bureau of Jingyuan County in Gansu.

The supervisors found wireless earphones as well as ruler and wristwatch-like receiving devices on the students, who were caught in three examination halls in Jingyuan County Monday and Tuesday, said the spokesman.

Police are investigating the cheating.

In a separate case in central China's Hubei Province, police Friday detained four people who sold wireless communication facilities to help students cheat in the college entrance exam.

The police confiscated 11 sets of devices worth more than 100,000 yuan (14,640 U.S. dollars), according to the public security bureau of Honghu City.

The suspects allegedly charged a 2,000-yuan deposit for each set of devices. After the examination, the buyers were to have paid another 5,000 yuan, it said.

The annual two-day exam, or "gaokao" in Chinese, is the only opportunity for high school students to win a place at university, making it the most important test most will ever sit in their lives.

More than 9.57 million people sat this year's exam and about 6.57 million will be enrolled at the nation's universities.