A new online system designed to make it easier for people to buy train tickets home for the Lunar New Year is struggling to cope with huge demand from millions of travellers across China.

The week-long holiday, also known as the Spring Festival, is the world's biggest annual migration of people as more than 200 million board trains and buses across the vast nation to celebrate with their families.

The railway ministry had hoped the online booking system would make it easier for China's migrant workers, many of whom spend days queuing up at train stations, sometimes in freezing weather, to get a ticket.

Although the holiday officially begins on January 23, demand for tickets is high many weeks in advance. The festival travel season is expected to end on February 16.

Train tickets for the holiday went on sale Sunday, but many people have complained that website glitches have left them out of pocket and with no ticket -- if they were lucky enough to log on to the site.

"I paid 218 yuan ($34) for a ticket from Shanghai to Chengdu online. When I went to collect the ticket a railway official told me he could not find the sales record," Huang Siling told the Global Times.

Many travellers flooded social networking sites to vent their anger at spending hours trying to access the new system, only to find that tickets allocated for that day had already sold out.

"Three days on end rushing for a ticket. It's almost 10 o'clock and I still can't log on. What's going on?" one web user posted on weibo, the Chinese version of Twitter.

Officials have pledged to improve the website's design and increase the network bandwidth to handle the demand, as well as refund money to out-of-pocket travellers within 15 days, state media said.

But some travellers said they were very happy with the new system, which means they no longer have to leave their home to buy a ticket.

"This morning I bought a ticket from Beijing to Harbin while lying in bed. After three years of queuing overnight at the train station for tickets, this is a luxury for me," said Yuyebugui in a posting on weibo.