Millions of people are celebrating Lunar New Year, also known as Chinese New Year, the most important annual holiday in much of Asia.
The new year began in China at midnight, with firework displays and family gatherings.
It marked the opening of the year of the snake, taking over from the dragon.
In China, an estimated 200 million people have travelled to be with their families in what is considered the biggest mass human migration on Earth.
The holiday will continue throughout the week, with government offices and businesses shut down.
The snake has a mixed reputation in China. It is associated with wisdom, beauty and intelligence but also pride and anger.
Residents of Beijing braved freezing temperatures on Saturday night to let off fireworks, which are believed to ward off evil spirits.
However, the displays in the capital were reportedly more muted than in previous years, starting later at night than usual and ending earlier on Sunday morning.
The city authorities had asked people to set off fewer fireworks because of dangerous levels of air pollution and a high number of smoggy days during the past month.
There was a sharp reduction in the sale of fireworks in the city, with 260,000 boxes purchased in the five days leading up to the new year, a 37% drop compared with last year, according to the official Xinhua news agency.
City environmental bureau readings showed 2.5 microgram pollution levels well above the 200 mark in most parts of the city at midday on Sunday, but these were well below the readings of 700 seen in January. Last year's fireworks sent pollution levels as high as 1,500.
Saturday evening also saw an anticipated 700 million people watch state television's annual TV gala, a variety performance show in which Celine Dion sang her theme tune from the movie Titanic.
Our correspondent says that, according to one well-known Chinese songwriter, My Heart Will Go On is one of two English songs that are well known in China. The other is Happy Birthday.
The gala's producers were ordered to make the show a more low-key affair, in the wake of the new leadership's recent crackdown on corruption and official extravagance.
Before Saturday's celebrations began, Communist Party chief Xi Jinping, who will become president in March, paid a visit to subway construction workers in Beijing to thank them for their service.
"Migrant workers have been the labour force behind China's reform and opening up... so we must look after you properly," he said. "I hope the construction firm has organised some new year entertainment for you so you can have a happy holiday."
Premier Wen Jiabao, who steps down in March, meanwhile celebrated the evening with victims of earthquakes and landslides in western China, state TV reported.
In Taiwan, President Ma Ying-jeou handed out traditional red envelopes containing money - in this case one Taiwanese dollar ($0.03; £0.02) - to people at a temple in Taipei.
Fireworks were also let off in Sydney.
Australian Prime Minister Julia Gillard wished the 900,000 Australians of Chinese descent a "healthy and prosperous Year of the Snake" on Twitter.