The incident took place near Mahranapratap chowk of the Bilaspur town when the bus was heading towards Mangla polling station to drop polling staff for tomorrow's Lok Sabha polls under Bilaspur parliamentary constituency, Bilaspur district official Devendra Kesharwani said.
The bus carrying 30 polling personnel escorted by security personnel left for Mangla police station from ITI Building at Koni this afternoon.
On the way, when the bus was crossing Tifra overbridge, one of its tyres got punctured after which the driver immediately applied the emergency brake, but the vehicle did not stop.
The injured polling personnel were admitted to the district hospital and two of them whose heads were injured were referred to Chhattisgarh Institute of Medical Sciences (CIMS), he said.