A notice is displayed in a restaurant warning foreigners to register with the police upon their arrival in China, as part of beefed up security measures for the Olympic Games in Beijing [Images] on July 10, 2008.

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China has embarked on a wide-ranging security crackdown ahead of the Games, and has even deployed surface-to-air missile batteries near Olympic venues to defend against airborne terrorist attacks.

Authorities in the capital have also started to carry out checks in the subway, and airport security has been beefed up substantially.

China has long identified terrorism as the biggest threat to the Games and state media on Wednesday said police had shot dead five people who wanted to wage "holy war" in the troubled western region of Xinjiang, home to 8 million Muslim Uighurs.

China's Vice President Xi Jinping, on Wednesday, told the "Beijing Olympics [Images] and Paralympics Games-time Work Mobilisation Rally" at the Great Hall of the People that China must give its all in the last 30 days to ensure the August 8-24 Games were safe.

"A safe Olympics is the most significant symbol of a successful Olympics in Beijing, and also the most important symbol to display the national image of China," he said.

"The existing security system must further intensify its comprehensive drilling and practice to constantly improve. All departments must entirely carry out the security requests from the central government."

Xi, the heir apparent to Chinese President Hu Jintao, said the coordination of Beijing and its surrounding provinces and contingency plans for security incidents were priorities.

Photograph: MARK RALSTON/AFP/Getty Images