  Supermassive stars (SMSs) of mass $\gtrsim 10^5 M_\odot$ are candidates for
seeds of supermassive black holes found in the center of many massive galaxies.
We simulate the gravitational collapse of a rigidly rotating SMS core including
nuclear burning effects in axisymmetric numerical-relativity simulation. We
find that for realistic initial conditions, the nuclear burning does not play
an important role. After the collapse, a torus surrounding a rotating black
hole is formed and a fraction of the torus material is ejected. We
quantitatively study the relation between the properties of these objects and
rotation. We find that if a SMS core is sufficiently rapidly rotating, the
torus and outflow mass have approximately $6\%$ and $1\%$ of the initial mass,
respectively. The typical average velocity and the total kinetic energy of the
outflow are $0.2~c$ and $10^{54-56}$ erg where $c$ is the speed of light.
Finally, we briefly discuss the possibility for observing the torus and
outflow.
