Date: 201706
Local time of day: 1801-2400
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Light: Night
Aircraft: B747 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Cruise
ATC / advisory: Center ZZZZ
Aircraft component: Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Diverted
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While at cruise on a Maintenance Ferry Flight; (4 pilots; no FAs or passengers) FL390; 350 NM east of ZZZZ; we received 'FIRE MAIN DECK' message on primary EICAS; coupled with two CAUTION messages; and five STATUS messages. Captain immediately reviewed QRH for relevant checklist; discovering there was none for FIRE MAIN DECK. Captain [advised ATC] as well as sent a report via CPDLC. Due to delay receiving clearance to divert to ZZZZ (nearest suitable airport) we began a 180 degree turn off track to the left; descending. 500 feet after cleared track 10 NM. I began broadcasting in the blind on 121.5; our call sign; position; our 180 degree turn north off track; nature of our problem; all whilst turning on all external lighting.  A flight came on frequency and offered assistance; I asked he relay to ATC we needed an immediate clearance to ZZZZ as we were a aircraft in distress due to cabin fire warnings.  We awoke Relief Pilots (who were on break) and informed of situation.  They immediately proceeded to the cabin armed with PBE (Personal Breathing Equipment) and flashlights to investigate. They thoroughly searched entire cabin; felt for heat on floors; walls; looking for smoke and searched the E&E compartment; finding no evidence of fire. Shortly thereafter; we received clearance from ATC for direct ZZZZZ intersection; FL390.  Captain contacted Dispatch and Maintenance Control to inform and obtain assistance on our warnings; cautions and messages.  I handled ATC comms and flew max speed to ZZZZ.  Relief Pilots took turns in each individually searching cabin for evidence of fire; smoke or heat; until we began descent for landing. Enroute to ZZZZ we reviewed Ditching Checklist and discussed Fire/Smoke removal Checklists should we discover a fire onboard.  Upon beginning our descent for landing; we flew max speed for the arrival and ILS to runway XXR at ZZZZ.  We landed without incident and were able to immediately clear runway whereupon ZZZZ Fire Department assessed our aircraft for evidence of fire.  Finding none we were cleared to taxi to the gate.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B747 flight crew reported diverting due to a FIRE MAIN DECK message during cruise. No evidence of fire was found from an inspection of the entire cabin and E&E compartment.