As millions of Chinese students are doing some last-minute cramming for the upcoming national college entrance examinations, authorities have launched a crackdown on sales of high-tech devices that might be used to cheat on the tests, which will be held across the country from June 7 to 9.

Since late April, police in Changchun, the capital city of northeastern China's Jilin Province, have busted eight criminal rings that have admitted to selling devices such as wireless earphones and transmitter-receiver sets that allow their buyers to cheat on the exams, said Liang Xiangdong, deputy head of the city's public security bureau.

Fourteen of the 18 arrested ring members are still in custody, Liang said.

The National College Entrance Examination (NCEE), or "gaokao," is the world's largest standardized test, taken by millions of Chinese students every year. However, a string of cheating scandals featuring the use of high-tech devices have cast a shadow over the test.

Wireless communication devices are used by some students to obtain answers from people outside of the examination venues.

In 2009, teachers in Jilin's city of Songyuan were found to be selling wireless devices to students, which sparked intense public outrage.

Public security authorities in Jilin and Gansu provinces have also begun intensifying identification checks of people living in hotels and rented homes near exam venues as they search for people running cheating-related businesses.

The Ministry of Education (MOE) has not yet issued the exact number of this year's NCEE examinees. Dai Jiagan, director of the examination center under the MOE, revealed on Thursday that about 9.33 million people will take the test in 310,000 exam halls across the country.