Olympic Delivery Authority chief executive David Higgins said the schedule could be affected by delays in acquiring the land needed for games' facilities.
Organizers are negotiating to relocate businesses that are based on the 202-hectare (500-acre) Olympic Park site in Stratford in east London. Ninety percent of the land is already secured but no work can begin until all the land needed is in public control.
"There is a considerable amount of work to carry out, let alone work commencing on the major facilities," Higgins told a public inquiry into the land purchases. "The timetable is extremely tight."
He said the land must be acquired by the summer of 2007, at the latest.
"This will enable demolition and remediation to take place alongside the installation of new services and infrastructure," Higgins said.
Construction of the Olympic Village would begin in early 2008, with work on the main stadium, aquatics and media facilities starting later that year.
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