Police said the toll might go up as the front portion of the bus was badly mangled and many were trapped inside.
The private Volvo bus coming from Hyderabad lost control, hit a road divider and fell into the canal between two bridges.
The driver of the bus was said to be a in a drowsy condition and thus lost control.
Deputy Chief Minister (Home) N China Rajappa has directed the Krishna district police to carry out rescue operations on a war-footing.
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