  We study the K\"ahler-Ricci flow on a class of projective bundles
$\mathbb{P}(\mathcal{O}_\Sigma \oplus L)$ over compact K\"ahler-Einstein
manifold $\Sigma^n$. Assuming the initial K\"ahler metric $\omega_0$ admits a
U(1)-invariant momentum profile, we give a criterion, characterized by the
triple $(\Sigma, L, [\omega_0])$, under which the $\mathbb{P}^1$-fiber
collapses along the K\"ahler-Ricci flow and the projective bundle converges to
$\Sigma$ in Gromov-Hausdorff sense. Furthermore, the K\"ahler-Ricci flow must
have Type I singularity and is of $(\C^n \times \mathbb{P}^1)$-type. This
generalizes and extends part of Song-Weinkove's work \cite{SgWk09} on
Hirzebruch surfaces.
