Average net effective office rents in core and fringe Central have fallen about 21 per cent in the past year, according to DTZ Debenham Tie Leung. DTZ expects to see a further 5 per cent to 10 per cent drop for the rest of the year due to cautious market sentiment and the global downturn. Research director Alva To forecast a bleak outlook for the office market in the next two quarters in view of the worldwide political turmoil. He said it would be difficult to predict timing of a turnaround unless the uncertainties arising from the attacks on Afghanistan were removed and there were clear signs of economic recovery in the United States. Mr To said many companies continued to downsize operations or put expansion plans on hold in the face of the unfavourable conditions. 'Several financial institutions delayed their tenancy negotiations with landlords following the tragic attacks in the US last month,' he said. DTZ said about 544,000 square feet of grade A office space on Hong Kong Island was surrendered in the third quarter. Vacant prime office rose slightly to 6.3 per cent, against 6.2 per cent in the second quarter. Rents in Central, Wan Chai and Causeway Bay recorded a 15 per cent fall in the third quarter from the second. Rents in Central and Admiralty stood at about HK$41 per square foot while rents at Wan Chai stayed at HK$24 per square foot. In Tsim Sha Tsui average rents fell 5 per cent to HK$21 per square foot. Rents on Island East dropped 8 per cent to HK$21 per square foot.