A shortage of prime office space will push up office rentals in the next six months, Vigers chairman Gareth Williams says. Future expansion plans of businesses would add to the scarcity of office space. 'I think for the next six months, you may see an upward [rental] movement because of the shortage of space, with the greatest rise seen in Central,' he said. Prime office rents on Hong Kong Island fell more slowly in July, as more businesses sought larger offices amid a market where supply was limited, according to the Vigers/Knight-Ridder Hong Kong Property Index. Net office rents in Central fell 12.4 per cent from levels in July last year, and Wan Chai north rents were down 13.8 per cent from a year ago. The index showed that Causeway Bay rents slipped 15.4 per cent. Month-on-month, Causeway Bay rents were also down 0.9 per cent after staying unchanged in the previous two months. Rents are not seen having much of an upside, as the Causeway Bay area faces increasing competition from new developments in Sheung Wan, Vigers said. In July, average office rents remained unchanged in Central at $63 per square foot and in Wan Chai north at $39.50 sq ft.