The 80,000-seater stadium, which will cost 496 million pounds, is not spectacular, designers said, but will offer a unique and "very tight, very compelling bowl".

The track and field area and lower tier of seating for 25,000 people will be sunk into the ground. The higher section, seating 55,000 people, will be taken down after the Games.

Food outlets and villages will also be on the so-called stadium island, which will be surrounded by water on three sides.

Media reports had suggested a roof would only cover VIP areas, but Rod Sheard, senior principal for the Team Stadium consortium of architects and builders, said two-thirds of spectators will be covered.

He said the design does not scream from the rooftops, and would not have a spectacular arch such as Wembley stadium in north London, but would impress with its complexity, and will help provide a special atmosphere.

"It is a very tight, very compelling bowl," he said.

"The atmosphere in this bowl, we think, will be pretty special."

It was a "clever building" providing a clever solution to the needs of a 21st-century stadium.

About 60,000 of the seats will be for the public during the Games, and the remaining 20,000 will be used by sponsors, the media and other organisations.

One of the reasons given by the Olympic Delivery Authority (ODA) last month for the 77 percent increase in the estimated cost of the main stadium, from its bid price of 280 million pounds, is its legacy and post-Games community use.

This will include a permanent athletics track and seating for 25,000 people, organisers said.

The ODA is in discussions with possible future tenants, including two rugby clubs and a football club.

ODA Chairman John Armitt said the stadium was inspiring and designed to be different.

"It is a fantastic example of British architecture and what construction companies can do."

Seb Coe, chairman of the London 2012 Organising Committee, said the stadium will be inspiring, innovative and sustainable.

"We talk about milestones, but few will be more exciting than this, the unveiling of the Olympic stadium, which will be the centre piece of our Olympic Park," he added.