The incident happened in Stockport at about 19:35 BST on Thursday after she had been dealing with congestion which had built up following a crash.
Greater Manchester Police (GMP) said the motorist "drove towards the PCSO" on the junction of Spring Gardens and Waterloo Road.
She is now recovering in hospital.
Police said the PCSO "tried to get out of the way" when the car came towards her but the driver then "mounted the kerb and knocked her over before continuing to drive off and making no attempts to stop".
Det Sgt David Chambers said: "A PCSO was knocked over in the line of duty whilst trying to assist with a collision and although she did sustain quite serious injuries, it could potentially have been a lot worse and thankfully she is now recovering well in hospital."
He appealed for witnesses to contact police, adding: "Nobody should have to worry about potentially being put in such a dangerous position when carrying out their job."
A Police Community Support Officer (PCSO) has been injured after a driver pulled out of traffic, mounted the kerb and knocked her over, police said.