Taratala: A state-owned bus possibly trying to jump a red light turned into an unguided missile at an intersection on Saturday morning, torpedoing an app cab going across its path and then a mini truck in the opposite flank before crashing into an office.

Five persons, including the three drivers, were injured in the serial collisions at the crossing of Diamond Harbour Road and Remount Road around 6am. Police said the outcome of the accident might have been far worse had it occurred a couple of hours later, by which time traffic volume would be higher.

An officer said it wasn't immediately clear from available CCTV footage if the signal had turned amber or red for the bus on route 7D (Sarsuna to Kankurgachi). But witnesses said the West Bengal State Corporation bus was travelling at speed and had jumped a red light at the crossing in front of the Ordnance Depot in Taratala.

"From what we know, the bus hit the right side of the Ola cab and swerved till the opposite flank, where it came at the mini truck head-on. The impact of the collision altered the direction of the bus towards a building on the right. The vehicle felled some guardrails and crashed into the closed iron shutters of the office," the officer said.

Ramraj Jaiswal, one of the directors of the transport company whose office the bus ploughed into, said he heard a bang and stepped out of his home in the same building to find three vehicles wrecked and a commotion around the intersection. "I also saw three persons bleeding. One of them was a woman (in the bus)," he recounted.

The police took the woman to the Calcutta Medical Research Institute, where she had a CT scan. An official at the hospital said the woman was discharged after first aid. The drivers of the state-owned bus and the app cab were taken to ESI Hospital at Thakurpukur. None of them required hospitalisation.

The bus driver, Ranjit Chakraborty, was later arrested and booked for "rash and negligent driving" and "causing grievous hurt by endangering someone's life", among other offences.

Two days ago, a water tanker belonging to the Calcutta Municipal Corporation had hit a 13-year-old girl on her way to school at Bansdroni. She is recuperating after surgery.

According to records maintained at Lalbazar, the city police headquarters, 275 state-owned buses had been prosecuted for traffic violations in Calcutta last year. The figure pales in comparison to 7.75 lakh private buses prosecuted in the same period.