The students, all approximately 24 years of age, had ulcers and blood clots inside their ears, apart from an unknown substance in the shape of a button battery, according to Gu, a doctor who treated the students.

"A student claimed that an earring had slipped into his ear," Gu said. "But when I took the 'earring' out, the student confessed that it was a mini wireless earphone that he planned to use for the upcoming College English Test."

One student even embedded two of the earphones in one ear. Another injured his eardrum and he had to have an operation to remove it, Gu said.

These earphones are allegedly very popular among college students. A typical package cost 800 yuan (US$99.63), in which the earphones cost 100 yuan (US$12.45) and the remaining 700 yuan (US$87.17) is for the exam answers. Some local earphone dealers also offer a service that links the earphones to the students' mobile phone for a slight fee.

Mini wireless earphones are considered restricted products and they are typically only used by TV announcers during broadcasts to relay reminders. Students are prohibited from using them, according to Jiangsu's provincial Bureau of Education.

College students' marks in the national College English Test are an important milestone which will influence both their graduation and future job-hunting success.