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 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, says Liang Xiangdong, deputy head of the city's public security bureau.

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

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.

High-tech wireless earphones have appeared at NCEE venues in recent years. The earphone is as slim as a match stick and can receive audio information.

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

In 2010, seven examinees from Gansu's county of Jingyuan were caught cheating using high-tech devices during the NCEE.

Public security authorities in provinces of Jilin and Gansu have begun intensifying identification checks of people living in hotels and rented homes near exam venues as they search for sellers of cheating devices and services.

In Gansu Province, examinees are forbidden from taking stationery into exam venues, and must only use those provided, according to the province's education authorities.

In Henan Province, watches cannot be taken into exam venues, and rubbers and rulers will be strictly inspected.

Test venues all over the country are gearing up with metal detectors, cell phone signal shielding devices and wireless mini earphones detectors.

The Ministry of Education (MOE) and the Ministry of Finance jointly-issued a notice early this year that states local financial authorities need to establish special funds to build standardized exam venues.

About 13,000 standardized exam venues, 3,500 exam papers confidential rooms and 365 command centers are planned to be completed by the end of 2012.

Dai Jiagan, director of the examination center under the MOE, revealed on Thursday that about 9.33 million students will take the national top test in 310,000 exam halls across the country.