The accident took place in Gonggar County, south of the regional capital of Lhasa, state-run Xinhua news agency reported.
The bus carrying 19 people belonged to a Lhasa-based tour company, it said.
The injured have been shifted to nearby hospitals and cause of the accident is being investigated.
Tibet is famous for its traditional Buddhist culture and tourism which has become a growing industry in recent decades.
The Himalayan region sees developing tourism as crucial to the economic future and has set a goal of attracting 15 million tourists a year by 2015, generating a revenue of up to USD 3 billion in a region with a population of 3 million, according to a report.