Why do pipes burst on freezing?

Water has a property of expanding while freezing. This property leads to an increase in the pressure exerted by water on the pipes. However, an important point that must be understood is that it's not always the outward pressure of water that leads to pipe burst. In case of complete blockage of pipe by ice, water gets trapped with ice at one end and a closed faucet at the other end. With increase in expansion and pressure, pipe ultimately gets blocked and bursts at the pipe's weakest point.