According to police, they received a call from locals that two persons had entered the manhole but did not come out.
The deceased were identified as Veera Swamy and Kotaiah, said Sulatanbazar inspector Shiva Shankar Rao.
"The bodies were sent for postmortem. It appears that they died due to inhalation of poisonous gas. We will get clear picture after postmortem," he said.
Rao said they are inquiring into who engaged them into the work.