They spotted the structure last evening, immediately stopped work and informed the contractors, police said.
Since there were houses on both sides of the road and also famous Kottai Eswaran Temple nearby, the contractors consulted the authorities and also the Archaeological department on whether to proceed with the works or not.
The department officials visited the spot and works were stopped.
Meanwhile, locals said they had heard from their ancestors that a tunnel goes under the centuries old temple, which was built by the rulers for escaping from their enemies during attacks.