Pushing through scores of passengers in the aisle of a cramped train at Beijing West station, Chen Guolan could barely contain her excitement at joining the world's largest annual human migration.

"I have been so busy working away all year, and now I will soon be seeing my family," she said to a group of strangers sitting alongside her as she began an epic 2,000 kilometre journey back to the quiet backwater she calls home.

Chen is one of China's hundreds of millions of migrant workers, who together make most of the 220 million train rides taken during the 40-day travel season before and after the Lunar New Year.

Around 7:30am she left the high-rise apartment where she works as a domestic worker for a family of seven in the capital, a city of more than 20 million people enduring sub-zero February temperatures and heavily polluted air.

Within 48 hours she would be beside her husband and son in the family home in a quiet, rugged area of the warmer south-western province of Sichuan, where the tree-capped mountains are hugged by mist, rather than toxic haze.

Chen had bought her 229 yuan ($37) ticket for the 10.35am to Chongqing two weeks earlier, joining millions who have clogged internet travel sites and queued at train stations to ensure they will be home for China's main national holiday.

Demand is phenomenal. For China's 236 million migrant workers, it is the only time of year they can see their families.

Chen, 50, failed to secure a bed in the train's sleeping compartment but had a seat for the 30-hour journey from Beijing West railway station to Chongqing North.

"I will be OK, I will just get my head down on the table when it is bedtime," she said.

Many were less fortunate, with 40 to 50 passengers forced to stand in each of the carriages, which seat about 120 people in total.

"I do not expect to sleep tonight. But then at least I got a ticket," said one heading for a village on the outskirts of Chongqing, crouching on the floor with two friends.

A group of four young men playing cards in a washing area between the carriages said they had not even contemplated how they would sleep.

"No problem. No problem," repeated one, laughing as he perched on the rim of a sink, cards in hand.

Meanwhile, Chen was in deep conversation with her neighbours. "We are speaking Sichuan dialect," she said, still grinning. "It is so nice to be able to speak my local dialect."

Chen speaks standard Mandarin Chinese during her working life in Beijing, where a typical salary for her job is around 2,500 yuan ($400) a month.

The train pulled into Chongqing on schedule at 4.27pm the following day, but she still had a five-hour bus journey to the city of Yibin ahead of her, followed by another 70 kilometres to the small rural town of Gongxian, and home.

In the moments before she finally arrived at 3am, her son and husband prepared a late-night dinner, the traditional Chinese welcome for a loved one returning from afar.

"I am so happy in my heart. My wife is returning home," said her 59-year-old husband Yuan Youjun, taking a break from cooking pork meatball soup and sliced pork cold-cuts with chilli seeds.

Chen's 23-year-old son Yuan Jinhao was also home from his job at a karaoke venue in a nearby town to welcome his mother.

"Chinese New Year is so important because we'll all be able to spend time together," he said, as he took a break from preparing steamed Chinese bread.

Meanwhile, clearly tired after almost two full days of travelling, Chen pulled her luggage up the hilly street to her home as the moment she had been waiting for all year neared.

With a warm hug she was welcomed inside, before being herded to the dinner table for the local delicacies her family had lovingly prepared.

After spending the year making food for others, it was a meal she had been warmly anticipating.

"The best thing about New Year is being with family. The old, the young. Everyone. I'm so happy," she said.