The Chinese are on the move.

Hundreds of millions of people have clamored aboard cars, buses, planes and trains to return to their hometowns for the Lunar New Year in an annual event that stretches the country's transport system to near its breaking point.

And they will be doing it in the warmest weather on record, according to the Beijing Meteorological Station, which said the temperature in Beijing on the eve of the festival would reach 10 degrees Celsius, making it the warmest festival eve since records began in 1951.

The Lunar New Year, or Spring Festival, starts on Sunday to usher in the year of the pig, but the Chinese have been preparing and boarding trains and planes for the last several weeks to go home for family reunions.

The travel strain has increased in recent years as tens of millions of migrant workers flood big cities such as Beijing and Shanghai in search of construction and other jobs.

Those types of workers cannot afford to fly, instead crowding into places like the Beijing West Train Station to board trains for trips that can take up to 35 hours.

"I am feeling very happy because I can join my family soon and I can see many old friends in my hometown. We will celebrate a happy New Year together," said Liu Juanhong, a migrant worker in Beijing heading home to Henan province.

Liu is one of an estimated 155 million people who will travel by train during the holiday period, which is officially one week but lasts longer for some.

The People's Daily said the total number of trips - including by plane, train, ship and vehicle - could total more than 2 billion journeys during the 40 days around the holiday. To avoid the crunch many people leave early or return late.

Chinese media has reported in the past that because of the crunch on the trains, some people have bought adult diapers to avoid the long lines outside the often stinking toilets.

Airlines were expected to have run more than 4,000 flights during these two weeks leading up to New Year, with the departure area of the Beijing airport brimming with travelers.

"I go back home every Chinese New Year. It is very important for Chinese just as Christmas is for Westerners," said Wu Xingbiao at the Beijing airport.

Police also issued cautions warning people to be careful of pickpockets. Travelers often carry large amounts of money to give as "hong bao," or red envelopes filled with cash, to children.

State television on Saturday showed police pulling one thief off a train in handcuffs.

For those who cannot be near friends will send messages through their mobile phones, the official Xinhua News Agency said, with an average of 40 million New Year messages an hour sent on Saturday.

But Xinhua said there were also warnings to students to not give each other pornographic New Year cards. "The cards are full of erotic pictures and flirtatious words," it said.

The government has extended the length of the official holiday to one week in recent years to encourage tourism as an economic development measure.