The world's largest annual migration began Saturday in China with tens of thousands in the capital boarding trains to journey home for next month's Lunar New Year celebrations.

Passengers will log 220 million train rides during the 40-day travel season, the Ministry of Railways estimates, as they criss-cross the country to celebrate with their families on February 10.

Many spend weeks at home for the most important holiday of the Chinese calendar, with the travel period spanning about two weeks before and after the Lunar New Year, also known as Spring Festival.

Travellers streamed into Beijing Railway Station on Saturday afternoon carrying heavy bags and boxes, while one man had strapped to his back a sack twice as thick and nearly as tall as him.

Just as making the trip home can be laborious -- often lasting one or two days -- so can simply acquiring a seat on the train, and every year complaints arise about the inefficiency or unfairness of the system.

For the second year in a row, New Year's travellers have been able to purchase tickets online and avoid long queues.

But those without Internet access were shut out while tech-savvy buyers used plug-ins and other software to facilitate purchases, leading some trips to sell out in minutes and prompting complaints.

One traveller heading home from Beijing to eastern Zhejiang province told AFP it took him seven days to book a ticket online, while a migrant worker said he did not even know how to use a computer.

But the thick queues at station counters commonplace in previous years were not seen on Saturday, and people mostly appeared to be picking up tickets before heading home.

Police, some armed with machine guns, kept watch over the massive flows of people. About 70,000 officers were deployed to train stations nationwide on Saturday, the Xinhua state news agency reported.