The first of two tall arches that will hold a spectacular 18,000 tonne steel and carbon panel roof above the main Athens Olympic stadium has been pushed into place.

Games organisers said the western arch, spanning 304 metres, covered a 70 metres distance before taking its final position around the Olympic stadium where the Games' opening and closing ceremonies and the athletics events will be held.

"The first part is done. Now we have the experience of the slide and the second arch will go faster," a government official told Reuters on Friday. "So the roof will be completed as planned."

The huge white arch was slid along steel tracks for three days before reaching its final position late on Thursday.

The long-awaited sliding of the 8,500 tonne western arch started on Monday, just 10 days before a May 20 deadline set by the International Olympic Committee (IOC) which had warned if it was not underway by then the project would be cancelled.

A second arch will also be moved into position in the coming days at the opposite side of the stadium so the latticed blue translucent roof, can cover the 55,000 seat arena.

Organisers hope the roof, designed by award-winning Spanish architect Santiago Calatrava, will become the Athens Games' architectural legacy.

Once finished the roof will be the capital's tallest structure towering 78 metres above the spectators.