The retail bank will exit its Sussex Street property in 2017 to move up the hill to the City core. In turn, Mirvac will leave to take up a lease at its 200 George Street office tower, currently under construction.

The round of musical chairs comes as the area near Wynyard is set to become the next construction zone. It will include the redevelopment of 1 Carrington Street, Wynyard train station, and the adjoining Wynyard Walk to Barangaroo and the pedestrianisation of George Street.

Mirvac confirmed its move last week, saying it will join Ernst & Young, which has leased 81 per cent of the property and is the anchor for 200 George Street.

Mirvac's chief executive Sudan Lloyd-Hurwitz said the move to the five floors of George Street was to "create an environment to support our people to work more effectively and collaboratively".

"Space in 200 George Street has been expertly designed to promote high levels of interaction and information sharing. Similar to our award-winning 8 Chifley office tower, floors at 200 George Street will be linked via a central atrium to create a vertically connected light-filled environment that supports flexibility, teamwork, collaboration and communication," Ms Lloyd-Hurwitz said of the relocation.

The new tower at 200 George Street is owned jointly by Mirvac Property Trust and the AMP Capital Wholesale Office Fund, but Mirvac has earmarked the adjoining properties at 210-220 George Street for sale as part of its capital "recycling" strategy.

The leasing activity comes as Asia Pacific witnessed the biggest decline in office occupancy costs during the past year, falling 8.3 per cent, according to DTZ's annual Global Office Thermometer.

An appreciating US dollar, weak economic growth in Europe, and significant new supply in emerging markets combined to erode costs across many global markets.

The DTZ  report also said that workstation costs, measured in local currencies, showed only a modest rise overall.

Dr Dominic Brown, Head of Asia Pacific research, said that within Asia Pacific, the large pipeline of supply in Indian markets has served to exacerbate local currency depreciation, while strong tenant demand in Tokyo has offset some of the currency effects.

"In Australia, weak fundamentals together with some depreciation in the Australian dollar has led to declines in excess of 12 per cent in USD terms in Brisbane and Perth," Dr Brown said.

But he said overall, in South Asia, Sydney and Singapore are the most expensive markets, with annual occupancy costs of nearly $US11,000.

He said international occupiers will continue to benefit from ebbing cost pressures in numerous office markets. Overall global occupancy costs are expected increase on average by just 0.5 per cent a year over the next two years (on a local currency basis).