One hundred firefighters battle to put out Sydney factory blaze

Firefighters have brought a factory fire under control in Sydney's northwest after it forced the evacuation of about 20 people from surrounding properties.

Police said emergency services were called to South Street in Rydalmere at about 2.30am today to find the pool products factory well alight.

Twenty-two fire trucks and 100 firefighters attended the blaze with fears the fire would spread to a neighbouring warehouse filled with paper and cardboard.

"We were very concerned that this massive fire would move to a warehouse to the rear, and a paper recycling plant (next door), this fire would have burned for days," Fire and Rescue NSW Commander Greg Mullins said.

No one is believed to have been in the building at the time.

Around 20 people were evacuated from surrounding buildings as a precaution, however authorities said the area is now safe.