There are reports that at least 10 people were killed when violence broke out after demonstrations in Tibet.
Protests are being held there because some people want Tibet to be free from Chinese rule.
But China says Tibet has always been part of its territory, and has given people behind the violence until Monday to give themselves up.
The riots are embarrassing for the government, which wants China to look good in time for the Olympic Games.
The 2008 Olympic games are being held in Beijing in five months time.
The violence, which is the worst in Tibet since 1989, broke out on Friday after four days of peaceful protests.