The McGowan government is set to radically overhaul the public sector with the number of government departments slashed by almost half.

Premier Mark McGowan said on Friday the number of state departments would reduce from 41 down to 25 by July 1 in the "biggest shakeup of the public sector in decades."

Premier Mark McGowan has unveiled the details of its public sector shake-up. Credit:Bohdan Warchomij

He said the government hadn't ruled out more departments getting abolished or merging down the track.

The Premier refused to say how many jobs would be lost across the public sector, but took to Twitter before the press conference claiming there would be job losses.