China has deployed surface-to-air missile launchers to protect the main venues for the Beijing Olympics from terrorist attack as part of one of the biggest – and most expensive – security operations in the country's history.

At least two Hongqi-7 missile launchers were visible today in a fenced military compound about 300 metres south of the Olympic Sports Center Stadium, a venue for soccer and modern pentathlon.

The compound is also within half a mile of the Water Cube aquatic centre and the Bird's Nest national stadium - the 225 million pound venue of the Games' opening ceremony.

Dozens of uniformed air force personnel were seen patrolling the compound's seven foot high mesh fence, which had a notice posted on it saying: "Military Administrative District No Admittance." Radar dishes and other military vehicles were also visible inside the compound.

China rarely allows its public to see such hardware – except during military parades and on television – but it was clearly no accident that the missile launchers were so visible.

Beijing is determined to show the world that it can handle all potential threats to an Olympics that will highlight China's emergence as a major world power.

Similar security measures were in place for the Athens Olympics four years ago with Patriot anti-aircraft missiles stationed around the city.

Neil Fergus, a security consultant for the Beijing Games, as well as the three previous ones, said that such precautions had been the norm since F-16 fighters patrolled the skies during the Atlanta Games in 1996.

"Sydney we did something similar but it really reached a particular, I suppose, a crescendo after 9/11," he told the Australian Broadcasting Corporation.

"So it is fairly complicated process but it does involve ultimately the possibility of extreme action being taken against any aviation interloper that is coming into the airspace."

The actual threat of an air attack on Beijing is limited as the airspace over Beijing is always restricted - even to commercial airliners. However, Olympic broadcasters will be allowed to use helicopters to cover the Games.

China also says that it faces a credible terrorist threat from separatists in its mainly Muslim northwestern region of Xinjiang – and from Tibet in the far west.

It says it has foiled at least three plots by Xinjiang militants to target the Olympics – including alleged attempts to crash an airliner and kidnap athletes and journalists.

It has also tightened security in the wake of anti-Chinese unrest in Tibet in March, which prompted a wave of pro-Tibet protests during the Olympic Torch's global relay.

Chinese officials said in April that the Dalai Lama, Tibet's exiled spiritual leader, and his followers, were plotting suicide attacks against China.

Human rights groups and pro-Tibet groups say the government is using the Olympics as an excuse to crack down on its critics even harder than usual.

Olympic officials have also expressed concern that China's security arrangements will spoil the Games' atmosphere.

However, Ronald Noble, the secretary general of Interpol, has said that there is a theoretical risk of an al Qaeda attack during the Games.

And China is not taking any chances, announcing last week that it had mobilized a 100,000-strong anti-terrorism force as well as 440,000 security guards and volunteers.

The force includes police commandos, regular army troops and the elite paramilitary Snow Wolf Commando Unit, which will handle terrorist alerts and public unrest.

"Experiences of past games show that terrorist attacks may occur before the games," the official Xinhua news agency quoted Liu Shaowu, security director for the Beijing Organizing Committee, as saying.

"So our anti-terrorist forces have been in action ahead of the opening ceremony."