A Sunshine Coast community has been "devastated" by the shooting murder of a popular 39-year-old man.

Auxiliary firefighter Peter Brady was shot dead outside a house on Tingira Close at Rainbow Beach around 6pm (AEST) Monday.

A murder investigation is underway and a 75-year-old man is assisting police with their inquiries.

Queensland Fire and Rescue Service (QFRS) area director Brad Schealler said Mr Brady's fellow firefighters and the Rainbow Beach community were shocked by the shooting.

"Whoever has done it has taken away the children's father, he has taken away a great civic member - it's just a terrible, terrible loss," he told AAP.

"Rainbow Beach is a very small community and in that community he was very highly regarded, he was extremely well known and this is a devastating blow to the entire community.

"We are very shocked and saddened at this sudden and tragic loss and our hearts go out very much to the family."

Supt Schealler said Mr Brady had been with the QFRS for 17 years and was captain of the Rainbow Beach Fire Brigade for 12 years until 2006 when he stepped down to concentrate more on his business interests.

He went "the extra yard" in his work as a firefighter, even using his own four-wheel drive to rescue people on occasion, Supt Schealler said.

Mr Brady received an Australia Day Award in 2003 for his dedication and leadership as a firefighter.

Supt Schealler said the fire service was not called to the shooting but several of Mr Brady's friends had gone to the scene.

Counselling was being arranged for his colleagues.