From sending SWAT teams into exam centers to arresting rule-breakers, China's public security authorities have been cracking down hard on college entrance examination cheaters who could face jail if caught.

This week's university entrance exam, whose origins date back to imperial China, determines which university students will attend and what major they're able to select - and as a result, much of their future.

This year, 9.4 million high school students have been taking the exam, known in China as the "gaokao", competing for few places in universities, state media reported.

Students caught cheating risk for the first time going to prison, the official Xinhua news agency said, possibly for as long as seven years.

Exam test papers were delivered by a police SWAT team in Beijing for the first time this year and at least eight police officers guarded each test center, state media reported.

Authorities are cracking down on wireless devices and substitute exam sitters in particular, according to Xinhua.

Police in the central province of Henan nabbed 9 people for selling fake exams, according to a local media report this week. Dozens of others had been caught elsewhere in the country, state media said. Most university hopefuls sit the two-day test simultaneously across the country. Chinese, maths and a foreign language are required. For students from rural homes, the exam has been praised as a leveler of the playing field and a catalyst for social mobility.

Xiong Bingqi, an expert at China's 21st Century Education Research Institute, told Reuters by phone that China would continue to hit back hard against cheaters and the scams that aid them.

"There's absolutely no doubt," he said. "Cheating on the gaokao exam diminishes the exam’s authoritativeness, and could even impact the credibility of the government."

"The government will take a whole series of measures to prevent that.”