By Luke Costin in Sydney

Footage of mangled bicycles surrounded by fire has been released after an e-bike factory went up in flames in suburban Sydney.

The blaze ignited in a small warehouse in Croydon about 5am, quickly engulfing the building situated behind a row of shops.

Firefighters needed to slice through a roller door and douse the fire from outside due to concerns parts of the structure may collapse.

Footage released by Fire and Rescue NSW on Friday showed embers raining down from the factory roof onto mangled bikes.

It also showed the charred remains of the warehouse after the roof appeared to have fallen in.

Some 60 firefighters battled for more than two hours to contain the fire, with some remaining on scene for several more hours to continue to douse hotspots.

They were being assisted by crews in aerial fire trucks.

No injuries have been reported.

The cause remains unknown with fire investigators due to enter the building once it is declared safe.

The blaze comes after the consumer watchdog recently warned about lithium-ion battery fires.

Li-ion fires are self-sustaining due to chain reactions inside the battery, making them hard to put out and allowing them to spontaneously reignite.

While rare given the number of devices on the market, the increasing prevalence of lithium-ion batteries in homes and businesses has raised the risk of serious fires due to storage and charging issues.

Fire authorities warn against using after-market or low-cost chargers, which can vary in quality.