Amitabh had visited the city on an invitation from the state government for the inaugural programme of the 23rd Kolkata International Film Festival and was going to the airport on Saturday morning when the accident took place.
"The wheel on the left rear-end of the Mercedes carrying Bachchan got detached from the vehicle on Dufferin Road when he was going to the airport to catch a flight for Mumbai on Saturday morning," a senior official at the secretariat confirmed the incident to PTI.
"The car was provided by a travel agency and we have show-caused it over the incident," he said adding that the agency was paid a huge amount for transporting the superstar.
The official said the initial probe revealed that the vehicle's "certificate of fitness" had expired long back but it was still in use.
According to a source in the secretariat, "proper action" might be taken against the agency if "any fault" on their part was found.
Bachchan was accompanied by a senior state minister in the car.
After the accident, the superstar was taken to the airport in the minister's vehicle that was following the Mercedes, a senior official of the Kolkata Traffic Police said.