  Long gamma-ray bursts (GRBs) are commonly accepted to originate in the
explosion of particularly massive stars, which gives rise to a highly
relativistic jet. Internal inhomogeneities in the expanding flow give rise to
internal shock waves that are believed to produce the gamma-rays we see. As the
jet travels further outward into the surrounding circumstellar medium
`external' shocks give rise to the afterglow emission seen in the X-ray,
optical and radio bands. Here we report on the early phases of the X-ray
emission of five GRBs. Their X-ray light curves are characterised by a rapid
fall-off for the first few hundred seconds, followed by a less rapid decline
lasting several hours. This steep decline, together with detailed spectral
properties of two particular bursts, shows that violent shock interactions take
place in the early jet outflows.
