Two firies injured battling Sydney fire

A fire at a restaurant on Sydney's north shore has been extinguished, with two firefighters treated at the scene for injuries sustained battling it.

Firefighters battle a blaze in Crows Nest, Sydney. (AAP)

Two firefighters have been injured battling a blaze that ripped through two buildings on Sydney's north shore.

The fire, on Alexander Street at Crows Nest, started in a restaurant about 11am on Saturday, before spreading to a real estate agent premises next door.

The fire, which has now been extinguished, forced the closure of part of the street and caused around five people to be evacuated.

Two firefighters were injured, one suffering a cut to his head and the other a back problem, Fire and Rescue NSW Superintendent Tom Cooper told AAP.

Both men were treated by paramedics at the scene.

Investigators were working to determine the cause of the blaze.

Supt Cooper said at this stage it was not thought to be suspicious.