The firefighter from Bundanoon Fire and Rescue NSW was called to a hotel with leading firefighter Adam Reeson, firefighter Stephen Edgar; and station officer Dennis Cornell.

The Southern Highland station responded to a Triple Zero call at about 3pm on Thursday, November 30, and when they arrived, were told the contractions were about a minute apart.

He helped guide the baby girl's birth and minutes later, she was delivered three weeks earlier than expected.

The firefighters also gained advice from paramedics through a joint first responder app.

"While you're there, you're concentrating on what you're told, you have a big responsibility," Mr Gnecchi-Ruscone said.

He was trained through the FRNSW's Community First Responder medical assistance program, which covers life-saving medical intervention.

Paramedics took the mum and bub to the hospital, where they are doing well.

The Southern Highlands firefighter, who works as an architect, was full of adrenaline and "complete euphoria".

"It was very exciting, it was a magical moment," he said.

The news of his efforts has spread around Bundanoon, and he has been given the nickname "midwife".

It is the first birth for the firefighter, and the station gifted the baby with a FRNSW bear as a memento.

The architect said it was the second time this year the station has helped with a birth - the first a couple of months ago in a Bundanoon public toilet.

They also assisted with a birth back in 2013.