Time is running out for Athens Olympics organisers to push a spectacular dome into place above the main Athens Olympic stadium with the deadline just two days away.

The International Olympic Committee has said the sliding of two huge arches, which will carry the weight of the 18,000 tonne steel roof, must take place by Wednesday otherwise the Games' architectural centrepice cannot be completed in time for the August 13-29 Games.

Organisers have postponed the sliding several times, including again on Monday, but with the project's completion date set for the end of June, a month and a half before the Olympics start, there is no time to waste.

"There are still details that need to be sorted out in preparing for the sliding and we also have to take into account the weather because, if it is windy, then that could cause problems," a government official told Reuters on Monday.

"It's still not decided exactly when the sliding will start."

Despite rushing to complete dozens of key Olympic venues and facing growing international concern over the Games' readiness, the roof, almost as tall as Sydney Harbour Bridge, remains the organisers' biggest challenge.

The steel dome, designed by acclaimed Spanish architect Santiago Calatrava, while not an official Olympic project, is meant to be the Games' architectural landmark and a spectacular backdrop for broadcasters.

Spread across the stadium like a spider's web with its translucent blue panels "lighting up the night", it is seen by architects from around the world as an engineering challenge bordering on the impossible.

After years of delays in signing the contract and getting work started, more than 250 workers, using some of the most advanced machinery in the world, are now preparing the ground for the sliding.

The IOC has said the whole project must be finished by June otherwise it would cause irreparable damage to the Olympic schedule.

The 150 million euro ($177 million) dome is more than just cosmetic surgery for the grimy Athens landscape.

The roof, soon to become the capital's tallest structure, will carry an additional 1,000 tonnes of essential telecommunications and security equipment and its blue carbon panels will reduce soaring summer heat by absorbing solar and thermal rays by about 45 per cent.

Weighing as much as 180 four-bedroom apartments, the roof has been designed to withstand massive eight Richter scale earthquakes and winds reaching 120 kilometres.