James Storer wrote: "RIP brother ... One of the best guys you would ever meet, with a young family, love you brother."
St George was also a member of Full Circle MMA, a martial arts school in Wollongong, New South Wales, where he used to live.
"Very sad to hear the news of the passing of one of our old members and great friend to myself and Full Circle MMA. Beau St George you will be greatly missed, your dry humour and quick wit. Your intensity in the gym, your work ethic. You were a great man, you will be greatly missed. Thoughts and prayers go out to everybody affected by this tragic loss," the club said in a tribute post.
St George had attended Whangarei Boys' High School.
A Ministry of Foreign Affairs spokesman said the ministry was aware of the death of a New Zealand citizen in France.
Multiple local French news websites are reporting the death in a head-on crash between two cars shortly before 6am on Thursday (local time).
St George, reported to be the driver, had died despite efforts by emergency services to resuscitate him.
Local media reported the accident happened in an area prone to accidents.
French police were unable to say at this stage what caused the accident.
French media reported the driver of the other car, a local man, also 33, received minor injuries and was transported to Manosque Hospital.