Not long after Tom Yam returned to his native Hong Kong after 40 years abroad, he picked Lantau Island to settle in, drawn to its laid-back villages, wooded trails and scenic beaches that seemed a world away from the bustle of the city.

That may be about to change with a plan to build artificial islands off Lantau to ease congestion in Hong Kong, ranked as the world's least affordable housing market for a ninth year by the U.S. research firm Demographia.

The East Lantau Metropolis, to be built on 1,700 hectares (6.6 square miles) of reclaimed land, will have a central business district and up to 400,000 housing units, with the first of an estimated 1.1 million residents expected to move in by 2032.