A worker with the Phuket Highways Office informed Wichit Police of a power outage inside the tunnel at around 7:40am.
Later inspecting the site, workers discovered that the outage was due to stolen electrical wires from the nearby control room. Wichit Police were called to the scene shortly before midday.
Officers, including forensic experts, investigated the scene and found a discarded helmet and flashlight, which are now being examined as evidence.
Wichit Police Chief Pol Col Chatree Chueakaew confirmed that an investigation is now underway, and police are working to identify suspects.