A number of vehicles travelling to Mumbai from Pune, rammed into one another, while a few others banged into the road dividers and the tunnel wall, police said.
According to them, due to the oil spilled on the road drivers lost control of their vehicles, which resulted in the multiple pileup.
Following the incident, traffic on the expressway was diverted to the old Mumbai-Pune highway, they added.
The work of removing the damaged vehicles from the Expressway was on and 14 cranes had been roped in for carrying out the task.