Narrative:

While at cruise; the first flight attendant called the cockpit to inform us that there was smoke in the cabin and that the mid-lavatory smoke detector was active. During the call; the flight attendant informed us that the smoke was getting thicker and that the aft lavatory smoke detectors were now active. The captain informed me (the first officer) to divert and asked where the closest field was. After informing the captain that ZZZ was the closest field; he declared an emergency with ATC and we began the descent. The captain coordinated with ATC; the flight attendants; and dispatch. We proceeded directly to ZZZ and were vectored to the ILS. The smoke seemed to dissipate and the smell seemed to dissipate; according to the flight attendant. Passing through 18000 ft; the flight attendant informed us that the smell had returned but that the smoke was still dissipating. The captain requested for the fire response equipment meet us after we clear the runway. Taxied to the gate to park. Deplaned using the jetway. Callback conversation with reporter revealed the following information: the reporter could add no further information as to what caused the smoke and no circuit breakers were noted to have tripped. The smoke seemed to dissipate as the aircraft descended.

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Original NASA ASRS Text

Title: B757 FLT CREW IS INFORMED OF SMOKE IN THE CABIN AND LAV SMOKE DETECTOR ACTIVATED. EMERGENCY IS DECLARED WITH DIVERSION TO NEAREST SUITABLE ARPT.

Narrative: WHILE AT CRUISE; THE FIRST FLT ATTENDANT CALLED THE COCKPIT TO INFORM US THAT THERE WAS SMOKE IN THE CABIN AND THAT THE MID-LAVATORY SMOKE DETECTOR WAS ACTIVE. DURING THE CALL; THE FLT ATTENDANT INFORMED US THAT THE SMOKE WAS GETTING THICKER AND THAT THE AFT LAVATORY SMOKE DETECTORS WERE NOW ACTIVE. THE CAPT INFORMED ME (THE FO) TO DIVERT AND ASKED WHERE THE CLOSEST FIELD WAS. AFTER INFORMING THE CAPT THAT ZZZ WAS THE CLOSEST FIELD; HE DECLARED AN EMER WITH ATC AND WE BEGAN THE DSCNT. THE CAPT COORDINATED WITH ATC; THE FLT ATTENDANTS; AND DISPATCH. WE PROCEEDED DIRECTLY TO ZZZ AND WERE VECTORED TO THE ILS. THE SMOKE SEEMED TO DISSIPATE AND THE SMELL SEEMED TO DISSIPATE; ACCORDING TO THE FLT ATTENDANT. PASSING THROUGH 18000 FT; THE FLT ATTENDANT INFORMED US THAT THE SMELL HAD RETURNED BUT THAT THE SMOKE WAS STILL DISSIPATING. THE CAPT REQUESTED FOR THE FIRE RESPONSE EQUIP MEET US AFTER WE CLR THE RWY. TAXIED TO THE GATE TO PARK. DEPLANED USING THE JETWAY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER COULD ADD NO FURTHER INFORMATION AS TO WHAT CAUSED THE SMOKE AND NO CIRCUIT BREAKERS WERE NOTED TO HAVE TRIPPED. THE SMOKE SEEMED TO DISSIPATE AS THE ACFT DESCENDED.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.