He said it was likely that more would put in applications before the deadline of 26 October and that others might register for the second stage of the competition.
He said the judging panel would meet on 30 October and decisions on both stages would be made in November.
He said: "Once a decision has been made the chosen practice will then travel to Ghana for a further interview and meet with the president of Ghana."
One practice will be selected to act as project manager, responsible for choosing a developer and project team, and another practice chosen to submit a masterplan. This will include offices, roads, a hospital, a shopping centre, 2000 houses, and possibly a tram system for the city.
The practices that have registered are: Robert Sarkodee-Adoo, Elsie Owusu, Knak Design, Kuma Environmental Design, Joseph Amoa Nyrka and AG Samsom.