A321
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action; General Flight Cancelled / Delayed
Aircraft
During cruise at FL350 we heard a noise and then [noticed] a burning odor in the cockpit and also in the cabin according  to the flight attendants. Because the odor persisted and it was strong we diverted to [an alternate airport]. Descending and running the Smoke/Avionics/Fumes check list we got Avionics Vent ECAM message. Eventually the odor dissipated and we landed safely.Maintenance told us that they found the Avionics Vent Fan failed.
A321 pilot reported diverting to an alternate airport after noticing a burning odor.