According to Peter Studley, Dexus general manager, research, the Sydney CBD vacancy rate of 4.1 per cent is the lowest it has been in 18 years, with little supply coming through in the 2020 financial year.

''Demand for office space in the Melbourne CBD is benefiting from the strongest population growth in the country, with the vacancy rate of 3.7 per cent at a 10-year low,'' Mr Studley said.

Centuria's unlisted fund and Blackrock have appointed agents from Knight Frank and CBRE to sell the Zenith Centre, which comprises two buildings of a combined 44,102 square metres set across 21 levels.

The funds jointly bought the a-grade office tower in 2016 for $280 million and have undertaken some upgrades. It is fully let to Property NSW, Commonwealth Government of Australia, Lendlease and Sage.

According to Knight Frank’s Tyler Talbot, partner institutional sales, Sydney metro, The Zenith is expected to receive significant interest from local and offshore investors.

''The investment will show a purchaser a significant yield premium to both Sydney and north Sydney CBDs, while also capitalising on the continued strong Sydney metropolitan rent growth, driven by increased demand and the government’s record infrastructure spending,'' Mr Talbot said.

''Australia remains an attractive global investment destination with new capital inflows remaining solid for quality assets.''

The Zenith is located at 821 Pacific Highway, with access to Chatswood’s public transport links and surrounding amenities, said Michael Andrews, NSW state director, CBRE.

''The office vacancy in Chatswood is at its lowest levels since the year 2000 at about 5.5 per cent, however, with strong tenant demand and no new major commercial projects in the pipeline, vacancy is expected to continue to fall below 5 per cent by 2020,'' Mr Andrews said.

JLL’s annual Australian Office Investment Review & Outlook 2019  says the value proposition in Brisbane, Adelaide, Perth and Canberra is becoming more pronounced as prime grade yield spreads to Sydney and Melbourne and the risk-free rates are wider than long-term benchmarks.

On the investment market, JLL analysis shows that the Sydney and Melbourne office markets represent 78 per cent ($226 billion) of Australia’s office market investable universe, valued at $288 billion in total.

However, JLL’s head of office investments, Australia, Rob Sewell, predicts 2019 will bring a more diverse pool of overseas investors into Australia and they will be looking for opportunities beyond Sydney and Melbourne.

''We are expecting office transaction volumes to be 10 per cent to 20 per cent lower in 2019,'' Mr Sewell said.

''We expect the Sydney and Melbourne markets to be development-led opportunities. The emerging development pipeline in some office markets will generate fund-through or take out opportunities for core capital sources.

''This will be the primary source of core long-dated lease product across Sydney and Melbourne in 2019.''