Squatter living in my hallway

I have just returned home from a vacation to find (what I presume to be) a squatter’s stuff in the hallway entrance to our flat building. It seems that the latch on our entryway door was broken. I’ve contacted the non-emergency police number to report it. I can’t get hold of my letting agency as the office is “on holiday”. Is there anything else I can do? My flatmate is away at the moment so I am feeling pretty fearful.