This month, officials said the Ballarat Base Hospital redevelopment - the biggest infrastructure project in the pipeline for the city - will not end until late 2027.

The delay comes as official data published by the Australian Institute of Health and Welfare (AIHW) shows an increasing number of emergency, urgent and semi-urgent patients are not being seen on time at the hospital.

A previous schedule published with the Treasury's 2019-20 budget said the upgrade - which now has a budget of $546.1 million - would finish by June 2026.

News of the delay emerged this month in the state parliament's Public Accounts and Estimates Committee Inquiry.

Initially, a department of health public servant stated the project was on time and on budget. However, a further response published last week confirmed a revised new completion date of late 2027.

The works, which are due to start this year and take place in three stages, now include an extra $80 million for a central energy plant to shore up the hospital's energy requirements both during the upgrade and beyond.

Tender documents released in December show the need for extra energy capacity became clear following "more detailed planning activities" since the announcement of an initial budget of $461.6 million in May 2018. The facility would be "critical to the functioning of the hospital", the tender says.

A multi-level tower with a new emergency department, as well as a women and children's hub, a new theatre suite and 100 more inpatient and short-stay beds are among the plans for the works. The project will also expand critical care facilities. These works will provide an intensive care unit, operating theatres, procedure rooms, endoscopy suites and consulting rooms.

The state government has said the works will allow 4000 more surgeries at the hospital every year, and permit the treatment of at least 18,000 more emergency patients and 14,500 inpatients annually.

The delay means the extra capacity will not be fully realised until the project's completion.

The central energy plant is part of the stage two works, which are scheduled to take place over 2022 to 2024.

The main works, which will include the demolition of the Edward Wilson Building and construction, are due from 2024 to 2027.

The shadow minister for health, Georgie Crozier, said the delay showed the Andrews government was "leaving healthcare needs behind" in the regions.

According to official data published by the AIHW, there has been a huge increase in the number of urgent and emergency patients treated at the hospital.

At busy times in recent years, the hospital has occasionally warned of delays for all but the most urgent patients.

In the past nine years, the number of emergency patients treated at the hospital has almost tripled. In 2011-12, official data shows there were 3406 emergency patients treated on site on time - stated as requiring treatment within 10 minutes - with 80 per cent of those treated on time - roughly on par with other large regional hospitals.

By comparison in 2019-20, there were 9699 emergency patients with 56 per cent of those treated on time, compared to a peer group average of 77 per cent.

Urgent patients stood at 12,521 in 2011-12 of whom 82 per cent were seen within the 30-minute recommended timeframe - higher than the average for comparable hospitals. In 2019-20, that stood at 22,265 with 62 per cent being treated within the same timeframe - well short of the 75 per cent peer average.

In the same timeframe, there has been a significant drop in the number of non-urgent patients treated at the hospital - 7551 in 2011-12 to 2426 in the last full financial year.

All of the 447 most urgent patients at the hospital - classified as 'resuscitation' - were treated immediately in 2019-20.

The Courier approached health minister Martin Foley for comment.

In the background to an emailed response, a government spokesperson said the project was "a complex job that requires considerable planning".

They said the works would "ensure the delivery minimises impacts to current services and to patients and families visiting the Ballarat Base Hospital".

If you are seeing this message you are a loyal digital subscriber to The Courier, as we made this story available only to subscribers. Thankyou very much for your support and allowing us to continue telling Ballarat's story. We appreciate your support of journalism in our great city.