How to get my dog to stop barking/lunging at people in my building?

I live in a 6 storey apartment block and I am having problems with my dog lunging and barking at anyone who dares walk in the communal corridors, use the lift of walk through the entrance at the same time of us.

I understand it’s his instinct to protect and he’s obviously confused thinking the whole building is ours rather than just my apartment.

However how can I discourage this in communal spaces? He is a small dog and I always have control of him and he’s never bit or anything but he does growl/bark very loudly and needs to be held back from lunging.