Urban planners can rewrite the rule book on high density living by making Hong Kong even denser, and they can start by going back to 15th century China, says the co-creator of a new exhibition on urban sprawl. Australian architect Ivan Rijavec said Beijing's Forbidden City was a leading example of high-density living and could provide the solution to Hong Kong's housing problems. "High density has now become the catchcry for sustainability," Rijavec said at yesterday's opening of a two-part exhibition, Now and When: Australian Urbanism, at the Central Library in Causeway Bay. "The Forbidden City had negative aspects of life in an urban environment, but one thing it did was to create the highest urban density that's ever been achieved," Rijavec said. Built during the Ming Dynasty in the early 1400s, the imperial palace covered more than 720,000 sq metres and boasted more than 8,700 rooms. "It could be a case of going back to the future," the Melbourne-based architect said. He said Hong Kong's density could be increased even further, with urban blocks amalgamated into super developments. "I don't think that's a frightening imagination of the future," he said. The exhibition features two sections. The "now" has images of five urban and non-urban regions in Australia, followed by the "when", which uses 3-D stereoscopic technology to show what cities may look like in 2050, ranging from the probable to the fantastic. One city is powered by mould; another features underwater pods that resurface when the weather suits and convert waves and tides into natural energy, while yet another imagines cities in the clouds with buildings hovering above existing street-level blocks. This latter idea would allow for cooler interior temperatures. "If you take the Le Corbusier quote that a house is a machine for living in, it follows that a city is a cultural and economic factory of a kind that enables all kinds of things to be possible," Rijavec said. He has been coming to Hong Kong since the 1970s and has witnessed the "blistering progress" of the city into an "extraordinary urban place". But he said it now needed to step up. "Our resources are limited, so we have to be careful how we construct our cities," he said. For Hong Kong to remain a leader in city planning, Rijavec said that it must keep pace with the rapid progress of mainland cities. "Up until the rise of mainland cities, Hong Kong was a maverick in the area of urban planning," he said. "It had a sophisticated approach to high-density living woven into comprehensive transport hubs and infrastructure. "But it really does have to be proactive to remain at the cutting edge; it won't be a stroll in the park." The exhibition, which made its debut at the 2010 Venice Biennale, will run until next Sunday.