One of western Sydney's busiest and most beleaguered hospitals will get a $576 million funding boost under a long-awaited upgrade announced by the Baird government.

Work on expanding Nepean Hospital’s emergency department will begin immediately, while an additional 200 beds, a dozen more operating theatres and a new neonatal intensive care unit will be built as part of the redevelopment.

The state government has been under increasing pressure this year from doctors who have warned the hospital is at “breaking point”, with the latest Bureau of Health Information figures revealing Nepean has the longest emergency department and elective surgery wait times in NSW.

The redevelopment is long overdue, Premier Mike Baird acknowledged on Monday, adding that it was the result of a “long-fought campaign”.

The government would work on ensuring the hospital had the capacity to deal with rising patient numbers in the next 20 years, he said.

“We strongly believe we can provide that,” he told reporters.

The $550 million rebuild, which will be entirely funded by the state government, includes a new helipad, 10 more birthing suites, more chemotherapy chairs, a new clinical services block and upgraded medical imaging unit.

An extra $26 million has also been allocated for a new 650-space car park.

Health Minister Jillian Skinner, who has previously been accused of neglecting the hospital, said the government had been working on getting the “planning right first”.

“Planning and ongoing consultation with stakeholders will continue through 2017 to ensure we deliver world-class facilities to the community and for our staff to work in,” she said.

Labor health spokesman Walt Secord said the opposition would be monitoring the development closely, after what he described as an announcement made by a government which had been “dragged kicking and screaming” by the community.

“We will be making sure the Baird government sticks to its timetable and actually delivers,” he said.

The NSW branch of the Australian Medical Association welcomed the “substantial” funding boost, and called for appropriate staffing numbers to also be guaranteed.

Major construction work at the hospital is expected to begin in 2018, with the hospital’s new clinical building due to be operational in 2021