The Turnbull government will provide an extra $84m to the Royal Flying Doctor Service to expand essential health services by providing mental health nurses for remote and rural areas.

On Thursday the prime minister, Malcolm Turnbull, and deputy prime minister Michael McCormack will be in Broken Hill to announce that the service will establish a mental health outreach clinic for the first time in its 90-year history.

In the 2018 budget the Turnbull government will provide a total of $327m over four years to ensure ambulance, dental and mental health services are extended to areas where commonwealth-funded activity currently doesn’t reach or is limited.

About $84m is new funding for psychologists and mental health nurses in a mental health outreach clinic program to begin operation by the start of next year.

Last year the Royal Flying Doctor service cared for 335,000 people including 36,799 air retrievals and 70,576 road transfers of patients.

Its chief executive, Martin Laverty, said the services’ aeromedical and dental services “now have certainty” with the extension of funding.

“We can now also deliver a new mental health service to underserved country areas in all states and the Northern Territory,” he said.

“All who live, work, and travel in country Australia can do so knowing the [Royal Flying Doctor Service] is on standby if needed, thanks to support of the Liberal-Nationals government.”

The chief executive of Mental Health Australia, Frank Quinlan said: “Remote Australians see mental health professionals at one fifth the rate of city people.

“Large parts of country Australia have no registered psychologists. This new funding for mental health care in remote Australia will help to fill that gap.”

The Royal Flying Doctor Service is celebrating its 90th birthday.

In a statement Turnbull said: “That’s 90 years of providing care to Australians living in some of the nation’s most remote areas, often in the most challenging circumstances.

“Ninety years of changing lives. Ninety years of saving lives.”