Calcutta, March 26: Four call centre employees in their 20s, three of them women, died in an early morning accident on EM Bypass today that has turned the spotlight on overworked drivers of office “cabs” that operate through the night.

Police said they were investigating whether the driver of the Tata Sumo, rented by the victims’ office, had fallen asleep at the wheel because of what he has described as his “punishing hours”.

Driver Debashis Yadav, though, said a truck had hit the Tata Sumo from behind around 4.30am, sending it crashing into the railings of a culvert. It then plunged 20 feet into a ditch and was smashed on impact.

“The car dangled from the railings for about half a minute before falling into the ditch,” Yadav said from his bed at RG Kar Hospital.

He added: “We have punishing hours. I had been driving since 11 at night with only one break of about 10 minutes. I had already driven about 300km overnight.”

The car had picked up nine employees of Aegis, an Essar Group company, from south Calcutta and was ferrying them for their 5am shift at their office in Salt Lake’s Sector V. One of the five surviving passengers, who have all been admitted to hospital, said the car was speeding to reach the office on time.

The acting deputy commissioner (traffic), Anjan Ganguly, said his department was verifying the driver’s statement. He said only a mechanical test would reveal the cause of the accident.

The police said Tapasee Pramanik, 26, Tanwi Dutta, 23, and Alpana Das, 24, were declared dead on arrival at Chittaranjan National Medical College Hospital. Amod Kumar Poddar, 25, died at the hospital. The three dead women were Calcuttans while Amod, a Bihar resident, was staying with his father and grandfather in the city.

Gunjan Sharma, centre head of Aegis, said two of the injured employees had been shifted to AMRI Hospitals, Salt Lake, and the other three to Columbia Asia. He said all five were “stable”.

Munmun Burman, sister of Mousumi Burman who is at AMRI, said: “My sister told me she was lucky to have survived. She said the car was travelling very fast, but she did not know how the accident happened.”

The impact flung eight of the ten occupants outside the car, said Prabir Mukherjee, an assistant sub-inspector of police from the Parama Investigation Centre who had reached the site about 10 minutes after the accident.

“I saw a couple of the injured trying to climb out of the ditch,” Mukherjee said. “We rushed to rescue them. Thankfully, some passing cars stopped and their occupants helped the rescue effort.”

The police and some local people climbed down into the ditch and took all the 10 dead and injured to hospital. After going through their identity cards, the police informed their families.

Animesh Pramanik, younger brother of Tapasee, said the family was informed over the phone around 5am.

“My father, mother and I rushed to the hospital only to find that my sister was dead. We are numb with shock. My sister had such a bright career ahead of her... it has been snuffed out now.”

Another early morning accident on EM Bypass last June had killed three youths and injured three of their friends. A lorry had mounted their Mitsubishi Lancer. That accident took place around 2.45am between Parama Island and Silver Spring.