A new report has found the source of more than half of New South Wales bus fires.

An inquiry into dozens of bus fires across the state found that the first wayward spark came from the engine bay.

The Office of Transport Safety Investigations (OTSI) covered 28 bus fires in NSW last year alone.

Several incidents involved the same bus on multiple occasions, leading to the destruction of some vehicles.

Incidents in one particular bus, which caught fire at Martins Creek and Beresfield, were found to be the result of electrical short-circuits in the alternator wiring.

The report into all 28 of the fires in 2013 said 16 the result of fires starting in the engine bay.

The impetus is clear, as it is in area where flammable liquids and gases come into contact with hot engine components. The report found loose fittings and damaged hose lines took fluids where they were not supposed to go, sparking the blazes.

Six fires were blamed on issues in wheel wells, with another five starting in the body section of the bus.

One fire was caused by arson.