BEIJING — The centerpiece of the Beijing Olympics rises 230 feet tall, its lattice of steel beams sometimes vanishing in a thick blanket of smog.

Quietly and without fanfare, officials have opened the National stadium, nicknamed the Bird’s Nest, and it’s ready to hatch its first sports event.

The final touches on the $450 million, 91,000-seat stadium won’t be completed until next month, but organizers let journalists in yesterday to look around. Inside, Franco Destefanis of Italy knelt as he installed the last few slabs of the rubberized running surface for track events.

“The design, the new-style architecture, and the size is impressive,” Mr. Destefanis, who has worked on 150 stadiums around the world and is doing his fifth straight Olympic track and field venue, said. “The outside catches your eye, particularly with the lights at night.”

Its unusual design was created by twisted steel beams that wrap around the exterior to resemble silver twigs binding a nest together. The icon of the Beijing Games, it’s been called the best work produced by Switzerland-based architects Jacques Herzog and Pierre de Meuron.

However, the Chinese artist Ai Weiwei, who was a consultant on the project, has since criticized it. He has likened the stadium to a “fake smile,” designed to hide social and political problems in China, which hopes to use the Olympics to show off its new political and economic power.

Of China’s 37 Olympic venues, the stadium is the last to be completed. There have been minor delays, although organizers have denied construction problems. They have said that preparing for the August 8 opening ceremony has required adjustments to building schedules, pushing back the stadium’s completion by a few months. Officials confirmed three months ago that two workers died during construction on the stadium, but denied press and broadcast reports that at least 10 had died.

In addition to the opening ceremony, the stadium hosts track and field events and the closing ceremony. The first event at the stadium will be on Friday and Saturday, a low-key race-walking meet. No glitzy ceremonies, political speeches, or fireworks are scheduled.

On the inside, the fancy exterior lattice work is hidden from view. The roof that partially extends over many of the seats is covered with a canvas-like material that will keep rain off most fans.