The extended lockdown plan for Melbourne could not have come at a worse time for the owners of CBD office buildings, as it coincides with the highest rate of sub-lease vacancies in the last nine years.

The city is a victim of its own success. A boom in new building development – outstripping every other city CBD – had enticed major corporates in Melbourne to expand into new office accommodation, leaving their old offices behind as backfill space. The merry-go-round stopped abruptly when the pandemic struck.

As old leases roll off that hidden vacancy of sub-lease could well translate into a very real problem for landlords, who are all too aware of what an over-supply of unoccupied space will do to their income.

Sub-lease vacancy is nearing 100,000 sq m, or 1.5 per cent of total CBD stock, well ahead of the 15-year average of 62,000 sq m, according to CBRE.

In the state government's road map for the return to normalcy, or "COVID normal", offices are the last cabs off the ranks. Office staff are unlikely to be back at their desks before early next year.