We report on the pressure-induced phase transition in a model of paracrystalline silicon (amorphous silicon with a crystalline grain) using an ab initio constant pressure simulation technique. The paracrystalline model transforms into a high-density amorphous phase at 16 GPa with a discontinuous volume change of similar to24%. The transformation of the crystalline grain begins at the boundary and proceeds into the core. We also study the pressure-induced crystallization of the network using the Gibbs free-energy calculation and find a transition from the paracrystalline silicon to beta-Sn at 3-4 GPa. The electronic nature of the pressure-induced semiconductor-metal transition is discussed.