Developers of the former marine police headquarters have been given a sweetener: they will be allowed to develop two storeys of attractions underground - alongside World War II tunnels dug by occupying Japanese forces. The move would allow whoever wins the tender for redevelopment of the 19th century complex in Tsim Sha Tsui to offset some of the costs of the project, the Tourism Commission said yesterday. The complex, built in 1883, comprises a main building, stables, signal tower and two former fire stations currently being used as a handicraft shop. Tendering for the development and running of the site as a tourist attraction opens today. The process will see the private sector putting forward ideas on how to put one of the SAR's oldest Victorian-style buildings to use as a modern tourist facility. Interested parties have until February 7 next year to submit their proposals and to quote a price to lease the site for 50 years. Assistant Commissioner for Tourism Erika Hui said that developers, while required to retain as many valuable features as possible, would be allowed to dig beneath the structures. 'Tentatively, two storeys could be built underground, which could be able to better sustain the whole project,' Mrs Hui said. She said the headquarters' buildings must be retained in any development. No new houses could be built within the site in keeping with the nature and historical value of the structures. The Antiquities and Monuments Office said that about 50 items, such as staircases, door locks and the custody cells, were considered of greatest value. 'Not all of them must be kept as they are, but we will rate proposals taking into account the scale of preservation they would achieve,' a spokeswoman said. The headquarters was built in 1883 and in its early years guarded Hong Kong against pirates. Marine police moved to their new base in Sai Wan Ho in November 1996, and since then the historical buildings have been left vacant. Patrick Lau Sau-shing, Hong Kong Institute of Architects' president, urged the government not to make money the only consideration. 'The project is going to be expensive, as developers cannot build new houses, while digging is often costly,' he said. 'Given the downturn, if the government rates land premiums too high in assessment of proposals, good ideas may be forgone.'