Beijing, China - Unwashed, unfed and lacking sleep, thousands of Chinese queued for their last chance at Olympic tickets on Friday, with police straining to hold back the crowds who threatened to break barricades.

Prospective buyers have been limited to two tickets at the same competition, but officials have promised the last tranche holds tickets for events at every venue, if not every event.

'I've been here for 48 hours. I think everyone should be tired,' said one man surnamed Wang.

Like many, he wanted tickets for an event in the National Stadium, dubbed the Bird's Nest, or the National Aquatics Centre, known as the Water Cube, the two showpiece stadiums that have changed Beijing's landscape.

But between the intense heat and long wait, the crowds approaching 20,000 threatened to descend into chaos, with hundreds of police and paramilitary People's Armed Police forces struggling to keep order.

'If you queue patiently, you will be able to buy Olympic tickets that you will be satisfied with,' a police officer bellowed through a loudspeaker.

Long queues had already formed by Wednesday afternoon, a day after Olympic organisers announced the final tranche of 820,000 tickets would go on sale.

By Thursday, 10,000 people formed a line snaking hundreds of metres away from the booth that opened at 9am local time on Friday, many hunkering down inside tents or under umbrellas to shelter from stifling 35 degrees Celsius temperature.

Tickets for the Games range in price from 5,000 yuan (S$998) for the opening ceremony to just 30 yuan for the softball preliminaries.

Olympic authorities expect income of around US$140 million from ticket sales, state media have reported.

Beijing's sale of the 7 million-odd Olympic tickets on offer have been swift, but not without incident. Prospective buyers complained on blogs and Internet chat-rooms of not being able to complete purchases after the third batch of tickets was released in May.

The former Olympic ticketing chief was sacked last November after the ticketing website crashed on the opening day of the second round of sales.

The Beijing Games start on Aug 8. -- REUTERS