Chinese rail authorities offered 10,000 stranded Lunar New Year travellers free upgrades to high-speed trains Wednesday as they tackled a huge backlog of passengers stuck in Guangzhou by snow and ice.

The city is the capital of the southern province of Guangdong, which as China's manufacturing powerhouse is a major hub for the vast numbers of migrant workers who leave their homes in the countryside to labour in factories.

Many only return home once a year, when tradition dictates that all family members must gather before midnight on the eve of the Lunar New Year which falls on February 8 this time.

The phenomenon puts huge pressure on the country's transport infrastructure and a big freeze in north and central China worsened the situation this year.

Vast numbers were held up at two stations in Guangzhou when their outbound trains were many hours late reaching the city, with the crowds peaking at nearly 100,000 people at one point on Monday, local police said.

Around 33,000 were still stranded at Guangzhou station by midday Wednesday, state broadcaster China Central Television said.

Rail authorities called up four high-speed trains from other areas to run extra services to destinations north of the city to reduce the crowds, the Guangzhou Railway (Group) Corporation said in a statement.

High-speed tickets are much more expensive than ordinary trains but the delayed travellers would not be charged the difference, it said. Nearly 10,000 would benefit.

The Chinese government estimates that 2.91 billion trips will be taken over the holiday's 40-day travel season, in what is thought to be the largest yearly movement of people in the world.