After weeks of uncertainty about the struggling project, developer John B. Hynes III and Vornado Realty Trust have secured financing to proceed with construction on the 1.25-million-square-foot, mixed-used site that will include retail shops, condominiums, a hotel, and offices in the historic Filene’s department store building and a new 38-story tower next to it. The head of the company building the project, John F. Fish of Suffolk Construction Co., said he was told by the developers to ramp up construction work because the team had locked in funding. Fish said he did not know details of the funding and Hynes and Vornado declined to comment, so it is not known when and under what terms the developers obtained the funds. Hynes and Vornado are building a 495-foot tower with retail on the first four floors, 250 hotel rooms over eight floors, 475,000 square feet of office space and 166 condominiums on the top 12 floors. The project also includes a grocery store and about 300 underground parking spaces, according to documents filed with the city. The original Filene’s building, designated a landmark by the Boston Landmarks Commission, will be substantially preserved. The project will also preserve a 1905 structure at Franklin and Hawley streets. Two newer buildings on the property were demolished last year.