Office vacancy rates in the Sydney and Melbourne CBDs are more than double what they were a year ago, raising the prospect that some towers could drop in value by as much as 15 per cent as rents also fall.

With business confidence blunted by uncertainty during the pandemic, demand for space has faltered. Supply has effectively exceeded demand, with a negative net take-up of space of 193,700 sq m during the third quarter, according to figures compiled by JLL.