BEIJING (AFP) - - Police struggled on Friday to control surging crowds of more than 50,000 people desperate to grab the last Olympic tickets in Beijing, as a Hong Kong journalist trying to cover the chaos was detained.

Frustration boiled over as the fans -- many of whom had been queueing for two days -- jostled to maintain their spot in the long line as latecomers tried to force their way into prime positions.

At one point the surging crowd broke through a control barrier and lurched towards the ticket counters, sparking a sharp reaction from police.

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

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

It was the last chance for Chinese to buy tickets for the Games, with 250,000 on sale at several locations in Beijing from 9:00am (0100 GMT) for events including athletics, diving, and gymnastics.

Demand was so high that more than 10,000 people were in a 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 ballooned to between 40,000 and 50,000 at that one line alone, Xiong said.

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

"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."

Amid the confrontations, an AFP reporter saw police manhandle and lead away Felix Wong, a photographer with Hong Kong's South China Morning Post. Staff at the newspaper's headquarters told AFP he was detained for several hours.

A Beijing Olympic spokeswoman confirmed to AFP that Wong was detained, but said it was because he was disobeying police orders to leave a restricted zone and had injured a police officer.

Despite the chaos, the sales did offer a once-in-a-lifetime opportunity to some fans, such as 23-year-old Lei Peng, who had slept on the footpath for two nights.

The engineering graduate from eastern China's Anhui province managed to score two seats to one of the hottest events of the Games -- the final of the men's 110m hurdles.

Chinese hopes for an athletics gold medal rest on defending Olympic and world champion 110m hurdler Liu Xiang.

"It was hard but worth it," said Lei, who had been queuing since midday on Wednesday.

Han Ruxiang, 76, had spent two nights sleeping on a bamboo mat so that he and his 67-year-old wife could see the finals of the diving competition.

"How can you be Chinese and not go to the Olympics when it is in China?" he said. "I am tired but so happy."

The demand has fuelled a flourishing black market in selling tickets at a massive profit, even though ticket touting has been outlawed. Police have arrested 60 touts over the past two months, according to state media reports.

Outside Beijing, 570,000 tickets for football matches went on sale in football competition host cities Tianjin, Shanghai, Qinhuangdao and Shenyang.

Altogether around seven million tickets were up for sale for the Games, with around 75 percent going to China's vast domestic audience, with the rest made available overseas through each country's National Olympic Committee.

Friday's release of tickets was the fourth and final round of sales for the August 8-24 Games.