At dawn the gates to the detention centre open. A truck laden with several tonnes of freshly dug garlic bulbs enters, and disappears into the vast complex, which houses both prisoners and people awaiting trial. For three hours, there is no movement apart from the Chinese police practising their morning drills.

Then the same truck emerges from the complex, its load replaced with cloves of peeled garlic. It drives for two hours to a depot in the central-eastern town of Jinxiang — the world’s garlic capital— which packages peeled garlic for export to India, according to a worker inside the facility.

Prison labour is common in China, where the law states that prisoners able to work must do so — a system known as “reform through labour”. China is home to around 2.3m prisoners and pre-trial detainees, according to the Institute for Criminal Policy Research, giving it the world’s second-largest prison population after the US.