A tourist visa is issued to those who come to China on holiday or are visiting relatives. Among several types of Chinese visas, this particular piece of paperwork is marked with the letter "L". This visa is designed for stays of a short duration – usually 30 and no more than 90 days. It can't be extended when it expires.
The Group visa, another type of tourist visa, is used by foreigners traveling in tour groups. The group visa is not displayed on individual passports but on a separate sheet of paper which requires the group enter and exit China together.
From November 15, 2000, visitors traveling to Hong Kong and Macao Special Administrative Regions (SARs) in tour groups organized by travel agencies registered in the SARs are exempted from visa requirements for a period of not exceeding six days when entering the following Chinese mainland cities: Guangzhou, Shenzhen, Zhuhai, Foshan, Dongguan, Zhongshan, Jiangmen, Zhaoqing, Huizhou and several others. The premise is that the traveler shall have the citizenship of a country having diplomatic relations with the People's Republic of China and carrying an ordinary passport.
Tip: If you're traveling to Lhasa from Kathmandu, you're best to get your Chinese visa in Kathmandu because although you may already have a visa issued in your home country you still have to get a visa in Kathmandu. This is regulated in an official memo between China and Nepal.
(Tibet Travel Expert)