A mobile tunnel boring unit is disclosed, comprising a support body driven by first drive means, the first drive means including a pair of spaced apart crawler tracks in contact with the tunnel floor and related track driving means to move the tracks. A cutter head drive means is located at an operatively front end of the boring unit, to which a rotatable cutter head can be fitted and rotatingly driven, in use, the cutter head comprising a full face cutter head fitted with cutters to bore a tunnel face. The cutter head is arranged to allow cuttings to pass through the cutter head for discharge into a muck hopper and onto a first conveyor arrangement, the cutter head drive means and a rear portion of the cutter head defining aligned central apertures to accommodate the muck hopper and a front part of the first conveyor arrangement. A telescopic shield arrangement is provided to shield the boring unit.