Violence broke out today among the 50,000 people queuing for tickets for the Olympics in Beijing as police struggled to control crowds who had been waiting in line for over two days.

At one point the surging crowd broke through a control barrier and lurched towards the ticket counters where the final batch of tickets for the Olympics, which begin next month, were about to go on sale.

In hot and dusty conditions, some groups in the crowd chanted insults at the police who were seen dragging people out of the line and kicking and punching them before leading them away.

Wang Zhongliang, a delivery worker for UPS said: "The police didn't have a clue how many people would come here and there was no organisation at all, it was chaos."

It was the last chance for the Chinese to buy tickets for the Games, and 250,000 went on sale at several locations in Beijing from 9:00am for events including athletics, diving, and gymnastics.

Demand was so high that more than 10,000 people were in the line by Thursday at one of the main ticket selling centres near the Olympic Stadium, district police chief Xiong Xingguo said.

By early Friday huge reinforcements of police were moved in to maintain order as numbers swelled to between 40,000 and 50,000, Xiong said.

Xiong conceded that police had been taken by surprise by the numbers.

"The situation was chaotic and difficult," he said. "Once the newspapers released the news about the ticket sale, too many people came at once so we had a security problem."

A Hong Kong journalist was detained by police on Friday while covering the chaotic scenes, organisers said.

Despite the pushing, jostling and discomfort, Xu Wengang, an information technology expert, said that he thought the method of ticket sales was fair.

"This way everybody gets a chance. But that's also the problem, because so many people came. It's a lot of trouble but it's fair," said Xu, 30, who was hoping to get tickets for the synchronised swimming.