A building in a central Auckland suburb has been destroyed by fire.

Fire crews responded to a blaze at a block of shops near Mt Albert Rd, in Royal Oak, after reports of an incident in the early hours of this morning.

It is understood emergency services were called to the area around 5.30am.

A worker at a nearby petrol station told the Herald the blaze was "pretty big" at its height just after 5am.

"I started at 5 o'clock, so it must've been around then.

Fire crews respond to a blaze in Royal Oak, central Auckland, early this morning. Photo / Michael Craig

"[Firefighters] were still putting it out about half an hour ago," he said just after 6.30am.

At the scene, firefighters could be seen moving around what is now a scorched skeleton of a building.

The circumstances of the fire are not yet known and it is unclear exactly what building it is.

Auckland Transport issued a travel alert just before 6.30am advising that some bus passengers will be affected by the blaze.

"Due to a fire near Royal Oak roundabout, Bus 30 is detouring and is expected to be delayed," the alert read.

Road authorities later said the bus service affected had since returned to its normal route.

This morning's blaze comes after firefighters battled a large commercial building fire in the industrial suburb of Penrose yesterday.