Authorities in China are employing surveillance drones in an effort to stamp out cheating in college entrance exams.

The stakes are high in the tests, with the scores determining which tier of university students can go to. Methods of cheating have included selling answers, hiring surrogate test takers and using wireless equipment to communicate during the test.

But this year officials have unleashed a six-propeller drone, flown over two testing centres in Luoyang in Henan province on Sunday – the first day of the exam – to scan for signals being sent to devices which may have been smuggled in. No such signals were detected, local reports said.

The drone cost hundreds of thousands of yuan – equivalent to tens of thousands of pounds – and is as big as a petrol station pump when extended, according to Lan Zhigang, from Luoyang’s radio supervision and regulation bureau.

Lan said: “A drone has its advantages. In an urban area full of tall buildings, various barriers limit the operating range of devices on ground, while the drone can rise up to 500 metres and detect signals over the whole city.”

Almost all Chinese high school graduates must take the test, with more than 9 million of them starting it on Sunday. Many students spend months cramming and parents travel to the cities where the tests are given to stay with them during the exam, which can last two or three days.

The education ministry said on Saturday that it had arrested 23 people since late May over attempts to arrange cheating. Students caught cheating can be barred from taking the test for up to three years.