That is what is commonly called 'tunneling' ...
Your cigar is tunneling when the inner filler is burning down, and the outer layers, including the wrapper and binder, are still unlit. There can be more than one of the channels, and they can be anywhere in the cigar (the side or the center). They make the cigar burn very bad, produce little smoke, burn hot and tend to go out.
Tunneling is normally found in cheaper daily type cigars. However, even the finest cigars may tunnel sometimes. There is not much you can do to save them when they start to tunnel. Slow down a little and hope it fixes itself. It can be caused by improperly lighting the cigar, or by smoking too quickly, puffing away like mad. The best way to fix this is to leave the cigar alone and let the outside catch up as soon as you notice it is happening. The sooner you "back off", the sooner the cigar will even up.
You can see the tunnel when you look at the foot. I have tried packing some burned ash into the tunnel but, I have had only very limited success. Also, if your cigar tunnels you can try to fix it by using your cutter and clipping down the unburned exterior and then try to relight the cigar.