Chinese students sat the annual make-or-break university entrance exams on Monday, with officials deploying drones or high-tech radio surveillance trucks at schools across the country to try and curb increasingly sophisticated cheating methods.

Nearly 10 million students will sit the crucially important two-day exam, known as the gaokao -- or "high test".

Authorities have become increasingly concerned about the risk of students using devices such as smart phones -- some of which have become smaller and easier to hide -- as an illicit aid during tests.

Beijing deployed 17,000 police officers to redirect traffic and increase security at the testing sites, and also set up service stations to treat anxious parents should any suffer heart attacks, the city government said in a statement.

The exam is the only method used to gain entry to the nation's universities which for poorer children can mean the difference between a white-collar office job and a life as a migrant labourer.

Officials in Luoyang, in Henan province purchased a drone designed to search for radio signals that could indicate cheating students, according to the Dahe News, the official provincial newspaper.

It will monitor signals from 500 metres above the test site, the paper said.

Photos on the website of the government-run China Daily showed radio engineering technicians using computers and scanning devices to search for signals that could be used to transmit answers to students.

A college student posing as someone else was caught at one test centre, and gave police the names of five other substitute test takers, according to the official Xinhua News Agency.

Security at test centres is extremely tight and in the past some schools have banned any metal from the exam room, leading to a prohibition on metal bra clasps.

In past years cheating devices have been found to be sewn into clothes.