For many, the chief challenge is just to buy a ticket for the journey. Most feel that they must be home by Saturday — in time for the lavish New Year’s Eve dinner.

The railway system groans under the weight of as many as four million travellers a day. Monday saw a record 3.8 million crowded on to China’s trains that chug slowly between cities as far apart as Harbin in the northeast and Kunming, about 30 hours away in the south.

Stations sell twice as many tickets as there are seats. Every space is filled. Travellers crouch on the floor, sleep in luggage racks and sit for hours in stinking lavatories. Using the toilet is out of the question.

Adult nappy sales are soaring — up by 50 per cent in some parts of southern China — as migrant workers prepare for 30-hour train journeys with no chance of a trip to the lavatory.

Li Tingting, 30, learnt the hard way. She remembers climbing over thousands of travellers as she searched for a toilet. She found none. She made the 19-hour journey from Beijing to her home in central Hunan province only by jumping off the train at one station and racing into a public toilet. “I climbed over so many people, but every space was full. I checked all the toilets. Next year I bought an adult nappy,” she said.

This year she will not be among the wave of humanity returning home.

She says her parents understand that the unpleasantness of the journey outweighs even the annual family reunion. This year China expects two billion journeys by plane, train, bus and ferry as exiles go home, travel among villages and then return to work. More than 120 million people — double the population of Britain — will travel.

Dozens of extra trains cannot cope with the migration. The more prosperous go by plane, but must still book weeks in advance. Booking a train ticket means queueing for as much as a day and a night. Airports and train stations are already scenes of chaos. China’s 140 million migrant workers — poor rural residents — have no choice but to queue for as long as it takes to buy a train ticket.

But while the poorest of China’s city residents may earn little more than £200 a year, they can probably afford an adult nappy.

They cost 20p each, to provide a little comfort and dignity on the journey.

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