BEIJING — A crowd of 30,000 people, baking in the heat and waiting for up to two days, swarmed a ticketing center Friday as the final batch of Olympic tickets went on sale. Police shoved and kicked them and used metal barricades to prevent a stampede.

The Aug. 8-24 Beijing Games are the first Olympics expected to be sold out, and some fans spent the night on thin bamboo mats and newspapers for a chance to buy the 250,000 tickets that went on sale in different parts of the city.

At the main ticket office not far from the national stadium known as the Bird's Nest, tempers flared as sticky bodies pressed against each other in the surging crowd before sales began at 9 a.m. Police yanked more than half a dozen unruly fans from the crowd, kicking one who fell as he was being led away and dragging another by his hair.

"It was very dangerous. I was afraid," said Wang Zhenqiang, who waited 28 hours with Ji Liqiang, a fellow businessman from eastern Shandong province, to buy tickets to the diving competition.

Hundreds of police and paramilitary troops tried to control the crowd, with lines of officers throwing their weight into hastily erected metal barricades to hold back the throng. There was no line; fans were allowed to pass through the police barricade in groups of 25 to 50, streaming toward the two-dozen-plus sales windows.

Scuffles broke out as officials opened additional windows at the last minute, causing some fans to stampede ahead of others.

"People got hurt around me. They fell and injured their knees and elbows. A barricade was bent out of shape by the crowd," Wang said.

In the scramble, Wang and his friend ended up with tickets to synchronized swimming, instead of the diving competition — where China is a gold-medal favorite.

"We all could see there would be a huge problem, and it became very chaotic," Ji said. "This also shows the Chinese government lacks the ability to deal with public crises."

Temperatures topped 93 degrees with 94 percent humidity on Friday, and some of the fans fainted in the heat. Some men stripped off their shirts during the long, muggy wait and police restraining the ticket buyers also handed out bottles of water.

Thousands also waited in western Beijing for 20,000 tickets for basketball. Another 570,000 tickets went on sale for preliminary round soccer matches in the cities of Tianjin, Shanghai, Shenyang and Qinhuangdao. There were no reports of major problems at the other sites.