Sources at two teams that unveiled designs on Wednesday said they expected that ideas or designs from more than one submission would be incorporated into the final scheme, which is due to be decided at the end of next month.
The shortlist of seven includes Foster and Partners and Foreign Office Architects. Foster's design has two 538 m interlinked towers that would form the tallest building in the world. The architect claimed that the "twinned" towers would be the world's most green and secure structure.
An architect on one of the teams said the issue of what to build on the site was too politically charged for a single winning design.
The architect said: "This competition won't decide anything. I can't believe they'll decide a winner."
This assessment was supported by New York consultants. Ray Crane, a former Arup USA chairman who heads the New York office of consulting engineer Meinhardt, said this was not a typical design contest.
He said: "It's not a competition to design the World Trade Centre, more a search for ideas. There will be a bit of mix-and-match when it comes to the decision."
Another US consultant added: "The competition is unlike anything that has gone before. It looks like whoever is successful will be asked to take on elements of the other ideas. The end result is not as important as everyone feeling their views have been considered."
The consultant added that infrastructure and transport work, such as a replacement subway station and tunnels, could not be carried out on the site until the outline of the buildings was decided.
The consultant said: "There is a push to get an agreement as to what should go on the site, so as to press ahead with the infrastructure."
Client the Lower Manhattan Development Corporation has stipulated that the site must include up to 1 million m2 of offices to replace the twin towers, as well as a hotel and shopping centre.
Crane said the World Trade Centre site would now form part of an overall redevelopment of the lower Manhattan area. He said: "The scope has changed during this competition. It's an all-encompassing development now."
New York mayor Michael Bloomberg last week outlined a £6.2bn redevelopment plan for lower Manhattan, which included new neighbourhoods, a reshaped Battery Park, a revamped waterfront area, a public marketplace and a tunnel.
He said: "No matter how magnificent the best designs for the 16 acres of the World Trade Centre site prove to be it must be complemented by an equally bold vision for all of lower Manhattan."