Organisers plan to start the slide of the first of two huge arches that will hold an 18,000 tonne roof above the revamped Olympic stadium at around 0900 GMT.

The IOC has warned organisers to start the final push before May 20 or scrap the 150 million euro ($179.8 million) project.

"The slide will start today, the western arch will be moved at a speed of five meters per hour," a government official told Reuters.

The arches will be moved a total of 71 meters in what is considered the most dangerous of all construction phases for the roof, a web-like white steel structure destined to become the Games' architectural trademark.

Many engineers have called the project a feat bordering on the impossible due to the sheer size of the arches and the weight of the roof.

"We are very confident because since Sunday this structure has been standing by itself without any support and that's the real important issue," an official from a main contractor involved in the work told Reuters.

IOC officials have said the three-day inspection will cover all outstanding preparation issues of the August 13-29 Games, which have been plagued by years of delays.

The IOC is expected to seek reassurances that work on several troubled projects, including the roof and two transport lines, are finally on track, a senior IOC official said.

"All members of the (inspection) commission would like to leave with a feeling of relief regarding preparations," Gilbert Felli, the IOC's Olympic Games Executive Director, told Reuters in an interview.

He said the inspectors will focus on problem projects such as the dome, which is holding back landscaping work, and the tram and suburban rail line.

"The IOC doesn't have more specific worries today than some months ago."

The suburban railroad and the tram line, which link the city with its international airport and the southern seaside Olympic sports venues, are still under construction and the Greek government promises to have them ready by the end of June.