BEIJING (AFP) - Beijing unveiled one of its Olympic stars here on Monday, an architectural gem designed to stage the swimming events at the Games in August.

The blue bubble-wrapped National Aquatics Centre, better known as the "Water Cube," took four years to build at a reported cost of 200 million dollars, most of it paid for by donations from overseas Chinese.

The squat box-like structure with three pools below ground level is made up of a steel skeleton sheathed in a Teflon-like plastic membrane that resembles bubbling water and gives the venue its name.

It stands in contrast to the other key Olympic venue close by -- the National Stadium or "Birds Nest", a curved structure made up of interlocking steam beams that is scheduled for opening in April or May.

"I am very moved and very proud," said Li Aiqing, president of Beijing's state-owned Asset Management Company, which owns the Water Cube, at a ceremony inaugurating the venue.

"This was a very ambitious project in terms of the construction technology, and a most difficult construction challenge."

The eco-friendly structure's translucent shell allows in natural sunlight, providing heat and light and cutting energy use by up to 30 percent, according to the Beijing Olympic organising committee.

However, China's notoriously poor air quality was evident at the ceremony.

Parts of the building's high-tech shell were covered by a film of grit while patches of grime could be seen in the interior membrane of the roof.

"Now its a bit dirty because of all the construction work around it," said Li. "But it will be fine after a clean-up."

The 17,000-seat venue will host swimming, diving, synchronised swimming and water polo during the August 8-24 Games and 42 gold medals will be awarded there.

It has a three-metre deep competition pool, a warm-up pool and a diving pool.

From Thursday, it will stage the six-day China Open, a swimming competition that will serve as a test of the venue ahead of the Olymics.

The building was unveiled a week after the launch of an investigation into claims that the deaths of more than 10 workers at the Bird's Nest had been covered up.

The Chinese government has denied any knowledge of the deaths reported a week ago by Britain's Sunday Times newspaper.

Yi Zhun, general manager for the builders of the Water Cube, said no workers had died building the swimming venue and he believed reports of deaths at the Bird's Nest were just rumour.

Olympic organisers have built or refurbished 37 venues, 31 of them in Beijing, which will stage the 28 sports during the Games.

More than half the Beijing venues, including the Water Cube, are concentrated in one small area in the north of the city known as the Olympic Green.

Four other cities will host the football tournament, yachting will take place in the Yellow Sea port city of Qingdao and Hong Kong is to stage the equestrian events.