A 140-year-old church near Geelong, southwest of Melbourne, has been destroyed in a ferocious fire overnight.

Firefighters were called to the blaze at St John The Evangelist Catholic Church on High Street in Bannockburn just after 4am and arrived to find the weatherboard church completely engulfed in flames.

"Some of the parish members have gone past already and expressed some concern," CFA spokesman Barry Planner said.

The 140-year-old church in Bannockburn was destroyed by fire overnight. (9NEWS) (9NEWS)

As well as the church itself, valuable items housed inside the building have also been completely destroyed.