One of the most keenly watched Olympic sports, gymnastics' defining moment at the Games came in 1976 in Montreal when Nadia Comaneci of Romania broke new ground by scoring a perfect 10 points.

Comaneci, now a US resident, has tipped China as the team to beat in Beijing, saying the home crowd will be urging on their gymnasts and expectations will be high.

"The Chinese team is very, very good," she said earlier this year. "In the men's competition, I don't think any other team could be better than them.

"The women's competition will be very close. Of course the best will win but it's a great advantage to have the Olympics in your country. You have a lot of support, which is great.

"It would be difficult for everybody else to get a hand on the medals."

China has a strong record at the gymnastics world championships but has struggled to reproduce its success on the Olympic stage.

The Chinese men won the team gold for the first time at the Sydney Games in 2000, but failed to build on the achievement in Athens, losing the title to arch-rival Japan.

They bounced back at the world gymnastics championships in Stuttgart last year, winning five golds, a performance that would provide a record haul for China if it could be repeated in Beijing.

The Japanese, who dominated men's gymnastics in the 1960s and 1970s, will be hoping to continue their Athens success in Beijing and usher in a new golden era.

Paul Hamm of the United States, the men's all-round champion four years ago, won't be defending his title after withdrawing last month because of a broken hand he sustained in May at the US Championships.

But his brother Morgan will be in Beijing having merely been warned, rather than banned after testing positive for a physician-prescribed anti-inflammatory medication without first seeking a therapeutic use exemption as required by global anti-doping rules.

Comaneci has picked out China's Yang Wei as the man to beat in Beijing and also highlighted the potential of US teenager Shawn Johnson in the women's competition.

Yang has seven world championship golds and was part of the men's team that won at the Sydney Olympics.

"Yang Wei is the favourite. He's the guy to beat," Paul Hamm said. "If Yang Wei has his most spectacular day, it's going to be very difficult to beat him."

Johnson, 16, is competing at her first Olympics after winning three golds at the world championships in Stuttgart.

Romania are again expected to be a major force after topping the overall medal tally in gymnastics in Athens.

All Romania's wins came from the women, but they will be without dual gold medallist Catalina Polor after she retired last year.

Russia, Ukraine and Germany are set to be in the running for medals.

Regardless of who takes the honours, changes to the scoring system introduced since Athens means there will be no perfect 10s like those pioneered by Comaneci.

Instead, gymnasts receive two scores -- one an open-ended mark measuring the difficulty of the routine, the other a mark out of 10 for how well it was executed.

In artistic gymnastics, men participate in six apparatus -- floor exercises, pommel horse, rings, vault, parallel bars and horizontal bar.