Nearly 26,000 desks sat empty in 2017 as the government reported agencies faced a lag between falling staff numbers and the chance to renegotiate leases to cut their office space.

The increase went against the trend in new figures from the Finance Department's latest report on occupancy in public service offices, which showed the government has continued to cut its floorspace since 2014.

A massive task awaits despite the progress as it continues leasing or owning nearly 2.9 million square metres of offices, more than 15 per cent of it empty.

There were 158,806 "work points" in its buildings and only 133,117 of them were occupied.

A spokeswoman for Finance Minister Mathias Cormann said more "work points" were occupied compared to 2014, and their number had decreased overall during the same period.

"It is inevitable that staff reductions or movements to other portfolio entities will result in a higher level of unoccupied work points due to the lead times involved in downsizing leased area commitments to align with the workforce," she said.

The Coalition has pushed ahead with lavish new government buildings despite the remaining vacant spaces, announcing in March new Armidale offices would host the Australian Pesticides and Veterinary Medicines Authority forced controversially to move north from Canberra amid accusations of pork barrelling.

A new Australian Taxation Office building opened in Gosford last month, and the Finance Department policing other agencies' real estate expenditure moved into a new state-of-the-art building in Canberra's inner south in 2016, in a deal set to cost $376 million over 20 years.

The former Immigration Department last year came under fire for its approach to the fit-out bill, believed to be the largest in Commonwealth history, for its new building in Canberra.

Senator Cormann's spokeswoman said its property management framework included a requirement that agencies fill surplus space before entering new leases.

"This has been a fundamental shift in the way Commonwealth property is managed," she said.

New figures show agencies continue offloading floorspace, bumping to 25 per cent the number of tenancies the government considers full enough, from 22 per cent in 2016, and nearly double the 13 per cent rate in the previous two years.

The government has reduced its floorspace by nearly 70,000 m² through its program to cut its unused real estate, called "Operation Tetris", which the Coalition says is on track to create $300 million in savings over 10 years.

Seventy per cent of the government's building leases are due to expire in the four years from July 2017, and the Coalition expects to further cut its floorspace and fill remaining offices with more public servants.

Among major agencies with too much space are the Australian Federal Police with 22.7 m² per person, the Department of Industry, Innovation and Science (20.7 m²), Health (18.8 m²), Defence (17.5 m²) and Immigration (17 m²).

The ACT had nearly half of the public service's office floorspace.

Public servants in Canberra had the most room to stretch out in Old Parliament House (141.7 m² per worker), the Family Court and Federal Circuit Court (50.2 m²) and the Australian Skills Quality Authority (39.1 m²).

Staff were squeezed most in ACT offices at the Australian Fisheries Management Authority (9.6 m²), the Royal Australian Mint (10.8 m²) and the Office of the Commonwealth Ombudsman (14 m²).