  We study a coronal mass ejection (CME) associated with an X-class flare,
whose initiation is clearly observed in low corona with high-cadence,
high-resolution EUV images, providing us a rare opportunity to witness the
early evolution of an energetic CME in detail. The eruption starts with a slow
expansion of cool overlying loops (~1 MK) following a jet-like event in the
periphery of the active region. Underneath the expanding loop system a reverse
S-shaped dimming is seen immediately above the brightening active region in hot
EUV passbands. The dimming is associated with a rising diffuse arch (~6 MK),
which we interpret as a preexistent, high-lying flux rope. This is followed by
the arising of a double hot channel (~10 MK) from the core of the active
region. The higher structures rise earlier and faster than lower ones, with the
leading front undergoing extremely rapid acceleration up to 35 km s$^2$. This
suggests that the torus instability is the major eruption mechanism and that it
is the high-lying flux rope rather than the hot channels that drives the
eruption. The compression of coronal plasmas skirting and overlying the
expanding loop system, whose aspect ratio $h/r$ increases with time as a result
of the rapid upward acceleration, plays a significant role in driving an
outward-propagating global EUV wave and a sunward-propagating local EUV wave,
respectively.
