Today, September 19th, is the day of the Mid-Autumn Festival that is widely celebrated in China and Vietnam, and the following day is a public holiday. It is a time when families traditionally get together to celebrate a good harvest. It coincides with the full moon on the 15th day of the eighth month of the Chinese calendar. It’s also called the Moon Festival because of the association with the full moon, or Mooncake Festival because these are eaten at this time. Typical mooncakes are round or rectangular pastries, measuring about 10 cm in diameter and 4–5 cm thick. This is the Cantonese mooncake, eaten in Southern China in Guangdong, Hong Kong, and Macau. A rich thick filling usually made from red bean or lotus seed paste is surrounded by a thin (2–3 mm) crust and may contain yolks from salted duck eggs. Mooncakes are usually eaten in small wedges accompanied by Chinese tea.
Here is a nice link with photographs of the festivities in Hong Kong, including a lantern exhibition and Fire Dragon dance performances.