Olympic officials have yet to throw any light on the sudden surge in security - in the form of armoured personnel carriers and soldiers - at venues around Beijing.
From early on Tuesday morning, armoured personnel carriers have been positioned at the security gates near the Birds Nest and Cube facilities, and directly outside the media centres.
Soldiers have also taken up positions at the gates to the athletes' village and many other Games venues.
Western journalists have been asking officials to explain the sudden military presence but have so far not been given any answers. A spokesperson for the Beijing Organising Committee would say only that the security level is not out of the ordinary.
New Zealand chef de mission Dave Currie says dramatic though the security changes sound, they are not as extreme as at Athens where there was a line of Exocet missile behind the Olympic village.
But Australian Olympic Committee president John Coates says China's preoccupation with security is dampening the atmosphere at the Games.
Mr Coates says China, as host country, has not been able to manage the balance between security and creating an enjoyable atmosphere.
Meanwhile, officials in Beijing have admitted to using busloads of people to fill Games venues with large numbers of empty seats. The said the cheer squads were necessary to create the right atmosphere during Games competitions.
All events taking place in Beijing are supposed to have been sold out, but a significant number of tickets are not being used.
Earlier, officials speculated that it might be that the preliminary rounds of some events were of less interest to spectators.