Beijing —- After the first few days of the Beijing Games, some cracks have appeared in China's perfect party: empty seats at the venues, disappointing crowds at the Olympic grounds, ticket scalping, a lack of buzz around the city and even official acknowledgment of trickery during the Opening Ceremony.

International Olympic Committee officials urged Beijing organizers Tuesday to let more people into the Olympic Green —- the centerpiece zone of the Games where most of the main venues are located —- and find ways to fill up the arenas.

"We've been saying, 'You're missing a great opportunity to get more of your people in here to celebrate your Games,' " said Kevan Gosper, vice chairman of the IOC's coordination commission for Beijing. "I would want to stress how important it is for the host city that the venues are seen to be full and everybody has the opportunity to enjoy the festivities."

Wang Wei, spokesman for the Beijing organizing committee, acknowledged there were not enough people in the green and that organizers were encouraging more to come.

The Olympics' global sponsors, who are each paying tens of millions of dollars to be associated with the Games, have complained that few visitors have been let through to see their pavilions.

"When I went out, there was a small trickle of people walking through," U.S. IOC member Bob Ctvrtlik said. "Access is difficult and security is incredibly tight. At some venues it's surprising when there have been sellouts and you see quite a few empty seats. At the stadiums you need warm enthusiastic crowds to help create an atmosphere for athletes to perform at their best."

Wang admitted that some empty seats were being filled by volunteers in yellow shirts serving as official cheerleaders.

"The responsibility lies with the local venue managers," he said. "If they find that there are not enough people, or if they find too many empty seats, they will organize some cheerleaders who are volunteers."

Meanwhile, it emerged that fake fireworks and lip-synching were part of Friday's spectacular Opening Ceremony —- an extravaganza watched by a global television audience that likely surpassed 2 billion viewers.

Fireworks bursting into the shape of 29 gigantic footprints were shown trudging above the Beijing skyline to the National Stadium near the start of the ceremony. Officials confirmed that some of the footage shown to TV viewers around the world and on giant screens inside the stadium featured a computer-generated, three-dimensional image.

"It was confirmed that previously recorded footage was provided to the broadcasters for convenience and theatrical effects —- as in many other big events," Wang said. "On the day of the ceremony there were actual footprints of fireworks from the south to the north of the city. However, because of the poor visibility of the night, some previously recorded footage may have been used."

In addition, the tiny, pigtailed 9-year-old girl in the red dress who sang "Ode to the Motherland" was lip-synching.

The real voice belonged to a 7-year-old girl who was replaced because she was deemed not cute enough by a member of China's Politburo.

"The national interest requires that the girl should have good looks and a good grasp of the song and look good on screen," the ceremony's chief music director, Chen Qigang, told Beijing Radio.

Since the Games started, other outside factors have undercut some of the hoped-for feel-good factor, including Saturday's fatal stabbing at a tourist site of a relative of the U.S. men's volleyball coach and the outbreak of hostilities between Russia and Georgia in South Ossettia. The fighting undermined the IOC's traditional call for observance of an "Olympic Truce" during the Games.