Construction has begun on the roof of London's showcase 2012 Olympic stadium.

The first 30-meter-long (98-foot-long) steel section has been lifted into place, bringing the height of the stadium so far to almost 37 meters (120 feet), the Olympic Delivery Authority said yesterday.

A huge crane was used to lift each 85-ton, 15-meter-high (50-foot) section and hold it in place while it was bolted to the top of the 27-meter (88-foot) high support columns for the roof that will cover the grandstands.

"The construction of the roof starts to give a real indication of the height of the structure and people can start to see for themselves how the Olympic Stadium will look during the games," ODA chairman John Armitt said. "This is a very complex engineering and construction project and we will still face challenges over the next year, but we have made a very strong start on the construction of this flagship venue."

Work on the stadium began last May. The venue will hold 85,000 spectators during the Olympics and will be scaled down to a 25,000-capacity venue after the games.