Seventeen thousand people are working on building projects

Twenty of the 31 competition venues are under construction with work well underway on the centre-piece National Stadium and the Aquatic centre.

"We thought we were ahead of schedule but there have been some problems," said chief economist Wang Zhiyuan.

Organisers explained that "applying new technologies" is proving difficult.

Construction chief Jun Yuan added: "We have adopted new technologies unprecedented in China. There are some problems on the technology resource side which we are trying to tackle."

We are considering what to do if it rains. But I'm hoping 8 August 2008 will be a propitious day Construction chief Jun Yuan

However, he denied that steel shortages - 110,000 tonnes are required for the National Stadium alone - were delaying the project.

"All the projects will be finished by the end of 2007, some of them by August or September 2007 to allow for testing," he said.

Sixteen of the hollow steel trusses that will hold in place the "Bird's Nest" roof of the 3.03 billion yuan (�216m) National Stadium are already clinging to the side of the concrete structure.

The equally-ambitious 1.02 billion yuan (�73m) Aquatic centre is at a less advanced stage.

Organisers are yet to decide what to do if it rains during the opening ceremony. They decided last year to abandon plans for a retractable roof for cost reasons.

"We are considering what to do if it rains," said Jun. "But I'm really hoping 8 August 2008 will be a propitious day."