The sales of 66 Goulburn Street, known as Civic Tower, in Sydney and 307 Queen Street, Brisbane, were flagged by GDI Property at its recent full-year results, when the group said its "asset management strategies" on the properties were nearing completion.

It comes at a time when city-based assets are in short supply but high demand, boosted by a rise in leasing deals.

The group's  managing director Steve Gillard said these management strategies entailed releasing work, where 11,000 square metres of the 14,300 sq m 2017 expiries at Goulburn Street have either been renewed or are subject to new or agreed leases. He added at Queen Street, the occupancy level has jumped to 87 per cent, including signed heads of agreement.

CBRE's​ Scott Gray-Spencer together with Knight Frank's John Bowie Wilson and Jonathan Vaughan will steer the campaign for the 24-level tower, above Sydney's Masonic Centre.

"It's a great opportunity to sell into a market with office vacancy contracting and increasing effective rents. There is also a distinct lack of investment opportunities with just one other major Sydney CBD asset currently available for sale," Mr Gray-Spencer said.

GDI Property exchanged contracts for the Civic Tower in 2014 for $136 million and it has been revalued to about $188 million.

Civic Tower was built in 2004 by Grocon and was the first building in Australia to be fully supported on a central lift core. The property has a 5.5 star NABERS​ energy rating.

Mr Gray-Spencer said the tower is well positioned to capitalise on the strong rental growth in Sydney's mid-town precinct.

Mr Bowie Wilson said the building's proximity to federal and state courts and retail amenity of World Square, positioned it to benefit from the major CBD infrastructure upgrades, including the Sydney Metro and CBD and South East Light Rail projects.

"The current strength in Sydney's office leasing market will help underpin buyer interest, providing an incoming owner with an immediate opportunity to add considerable value by leasing the remaining vacancy floors and leveraging the market moving forward," Mr Bowie Wilson said.

In Brisbane, the asset is valued at about $128 million and CBRE's Bruce Baker, Flint Davidson and Tom Phipps will steer the Queen Street sale campaign, which is tipped to generate significant investor interest.

"Well-positioned, core real estate is a rare commodity at present, with limited opportunities throughout the major capital city markets," Mr Baker said.

Other sale campaigns in Sydney include 333 Kent Street, 28 O'Connell Street and 183-185 Clarence Street, through Vince Kernahan, the national director of Sydney City Sales, Colliers International.