CRJ200 RECEIVES CABIN DOOR WARNINGS WHILE AT FL310. REQUEST DESCENT AND DURING DESCENT O2 MASKS DEPLOY. EMERGENCY DECLARED AND FLT DIVERTS TO ZZZ FOR LNDG.

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AT CRUISE ALT OF FL310; WE GOT A YELLOW 'SVC DOOR OPEN' CAS MESSAGE. I CALLED THE FLT ATTENDANT AND ASKED ABOUT THE DOOR CONDITION. HE SAID IT LOOKED AND SOUNDED NORMAL. DURING OUR CONVERSATION; WE GOT AN ADDITIONAL 'MAIN CABIN DOOR' RED CAS. I ASKED THE FLT ATTENDANT ABOUT THAT DOOR'S CONDITION AND HE SAID IT ALSO APPEARED NORMAL. BOTH CAS MESSAGES WERE LIGHTS ONLY WITH NO 'DOOR' VERBAL ALARM. WE THEN RAN THE QRH FOR THE DOOR LIGHTS AND I TOOK THE RADIOS AND ASKED FOR A NORMAL DSCNT TO 10000 FT. I WAS GIVEN A TURN OFF AIRWAY TO 090 DEGS EBOUND. DURING OUR DSCNT; WE GOT A 'CABIN ALT' RED CAS AND INITIATED IMMEDIATE ACTION ITEMS FOR AN EMER DSCNT. QRH WAS THEN AGAIN FOLLOWED AND COMPLETED. ATC WOULD ONLY GIVE ME 12000 FT ON THE DSCNT AND TOLD ME IF I WANTED TO DECLARE AN EMER; I COULD GET ANYTHING I WANTED. I DID AND CONTINUED TO 10000 FT AND LATER ASKED FOR 8000 FT AND DIRECT ZZZ. I WAS LATER ASKED IF I WANTED TO CONTINUE THE EMER INTO ZZZ AND AT THAT TIME; I CANCELED THE EMER DUE TO THE FACT WE WERE AT 8000 FT; DIRECT ZZZ; AND BACK TO NORMAL. DURING THE DSCNT; PAX OXYGEN MASKS AUTO-DEPLOYED AND THAT COMBINED WITH THE BURNING SMELL OF THE PAX OXYGEN GENERATORS UPSET SEVERAL PAX. I MADE SEVERAL ANNOUNCEMENTS TO TELL THEM THEY AND THE ACFT WERE SAFE AND WE WOULD LAND SOON AT ZZZ.