Students in central China have resorted to classroom intravenous drips as a study aid to prepare for the nation's notoriously difficult college entrance exams, state press said Tuesday.

Photos showing students at Xiaogang high school in Hubei province hooked up to hanging bottles of amino acids have gone viral on the web, eliciting shocked concern over how far Chinese students will go to get into university.

According to school official Gao Pingqiang, the pre-exam injection has become popular with the students as it has no harmful health effects and helps the students relax, the China Daily reported.

"The school will not suspend the injection and we will continue if students want it," the paper quoted Gao as saying.

Another school official told the paper the amino acids in the drip improved the physical condition of the students and boosted their energy levels.

Many in China's population of over 1.3 billion people have long viewed the June college entrance exams as a make-or-break test that can determine future careers and life paths.

The China Daily reported the government is investigating the intravenous drips, citing experts as saying such injections are unnecessary and could lead to infection.

Online bloggers were largely critical of the practise.

"The group intravenous medication by students does not mean the students are sick, it means that society is sick," said one posting on Sina Weibo, a Twitter-like microblog.

"This is just another act to cheat people, it is incredible that the school lacks basic knowledge, you know for sure that someone behind the scenes is making money from this," said another microblogger.