ACFT EQUIP PROB. ACR DIVERTS AND LANDS WITH SMOKE IN THE CABIN. DURING NIGHT OP.

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THE FLT WAS SCHEDULED FROM MSP TO TVC. IN CRUISE I NOTICED THE SMELL OF SMOKE AND ASKED THE CAPT IF HE SMELLED IT AS WELL; HE AGREED. I WAS THE PF SO HE PROCEEDED TO INVESTIGATE AND DETERMINED IT WAS COMING FROM THE CABIN. INITIALLY I SUSPECTED A NONCOMPLIANT PAX AS DID THE CAPT. HOWEVER; THERE WAS NO WAY TO DETERMINE THAT FACT. WITHIN A MATTER OF SECONDS THE SMOKE FILLED THE CABIN AND I CALLED FOR THE CREW MASKS AND EMER CHKLIST. THE CAPT; HOWEVER; WAS CONVINCED THAT IT WAS A PAX OR A CABIN FIRE AND GOT UP TO GO BACK AND INVESTIGATE LEAVING ME WITH THE ACFT WHICH I FEEL WAS POOR JUDGEMENT ON HIS PART -- TO IGNORE THE OBVIOUS AND POSSIBLY ENDANGER EVERYONE BY LEAVING HIS SEAT. I PUT ON MY MASK AND CONTINUED FLYING THE ACFT. WHEN HE CAME BACK WE EXECUTED THE SMOKE REMOVAL CHKLIST. HOWEVER; SMOKE CONTINUED TO FILL THE CABIN. WE HAD REQUESTED A DSCNT AND AFTER THE CHKLIST WAS COMPLETE THE CAPT DECLARED AN EMER AND REQUESTED THE APCH TO BEMIDJI; MN; THE NEAREST ARPT. THE FLT LANDED WITHOUT INCIDENT AND THE PAX DEPLANED. I FEEL THAT THE SAFETY OF THE FLT WAS COMPROMISED BY THE CAPT'S GENERAL CONFUSION AND REFUSAL TO ACKNOWLEDGE THE PROB. CONTRIBUTING FACTORS INCLUDE IMPAIRED COMS WITH THE OXYGEN MASKS ON AND THE FACT THAT BEING SO CLOSE TO THE ARPT WE WERE RUSHED. ALSO; WITH ACTUAL SMOKE IN THE ACFT; I FELT COMPELLED TO GET ON THE GND ASAP. NO TRAINING CAN PREPARE YOU FOR ACTUAL SMOKE. OF THE 7 PAX BRIEFED TO PUT ON THEIR OXYGEN MASKS; ONLY 4 DID; AND AFTER LNDG THEY COMPLAINED ABOUT NOT GETTING ENOUGH OXYGEN. HOWEVER; POSTFLT INSPECTION REVEALED THAT NONE OF THE MASKS WERE PLUGGED IN. PERHAPS THEY FELT THAT THE MASKS WERE UNNECESSARY OR WERE CONFUSED ABOUT PROPER USAGE; IE; NEEDED TO BE PLUGGED IN. THE SOURCE OF THE SMOKE WAS AN AIR CYCLE MACHINE ON THE R SIDE. THE CHKLIST CALLS FOR BLEED AIRS OFF WHICH WE DID. I THINK THAT WE JUST PERCEIVED THE SMOKE TO BE WORSE THAN REALITY AFTER COMPLETION OF THE CHKLIST.