As millions join the world's largest annual human migration, some in China will not return home for the Lunar New Year, fearing the rising costs of seasonal gifts and ridicule from their families.

Nanny and cleaner Tian earns 3,500 yuan ($580) a month looking after the children of an expat couple in Beijing, and has not seen her own family in two years.

But if she goes home to Henan province, 800 kilometres (500 miles) to the south, she will be expected to hand out just as much -- in red envelopes known as hongbao -- to non-working members of her extended family, especially children.

"I have many nieces and nephews and I really can't afford the amount I will have to pay for each of their hongbaos," said the 46-year-old, slurping noodle soup in a heated high-rise apartment.

Instead Tian -- who only wanted her surname used -- will stay in the capital, where she can earn a bonus of her own.

"Staying in Beijing I can make four or maybe five thousand yuan, and during public holidays I can get double pay on top of that," she added, looking downwards with a smile at fellow migrant workers waiting for buses in the cold street below, their belongings loaded on their backs.

The Lunar New Year, known as the Spring Festival in China, is the only time that many of China's 245 million migrants will see their families all year.

The country's rush to the cities is the greatest human movement in history, but has thrown up a range of social consequences, particularly for children "left behind" in the care of often elderly relatives.

Even so financial pressures in an increasingly wealthy but unequal society are such that a growing number of migrants are choosing to spend the festival at their place of work.

Embarrassment over low wages

Another nanny, who gave her surname as Lou, lamented the costs and trouble of the holidays ahead of a 1,600-kilometre coach journey back to the northwestern province of Gansu.

"It's not just the cost of the hongbaos, but I also have to travel to see all my family, which is a lot of time and cost as they are scattered across the countryside," said Lou, whose seat for the 21-hour journey cost her 217 yuan.

As Lou prepared for her gruelling trek from the booming capital to the dusty, arid backwater she calls home, some of China's poorest citizens were heading the other way in search of opportunity.

"We have had over 100 domestic workers turn up in the city just before the Spring Festival looking for work, which is far more than last year," said a woman surnamed Ge who works at a Beijing branch of national domestic cleaning agency Fuping.

"There is the demand, because not that many domestic workers stay in the city, and of course, the pay is better this time of year," she added.

About a third of China's migrants -- who mainly work in the construction, manufacturing and domestic servant industries -- do not return home for the New Year, according to a recent survey.

Almost a fifth of migrants who were staying at their workplace said it would be easier to find better work during the holiday period -- while another 18 percent said they were afraid of being ridiculed by parents for not having a girlfriend or boyfriend.

The same proportion cited the costs involved, according to the survey of 13,200 migrants from job hunting website daguu.com.

But the biggest single reason for not returning, at 36 percent, was embarrassment at having earned too little.

With average urban incomes around 2,500 yuan a month, the prospect of making twice that much is enough to delay seeing their relatives.

"I may go and see the family in the summer when I will have more money... and it won't be so cold then," said Tian, huddling against the radiator.