The LFB were called to Theobalds Road, near the junction with Southampton Row, just after 9.30am today (November 26).
10 fire engines and around 70 firefighters were called to the scene.
Crews discovered high-voltage electrical cables alight below street level, prompting a complex and hazardous operation.
Station Commander Paul Morgan said: “Due to the challenging nature of the incident, additional resources were requested.
“Once power was isolated, firefighters wearing breathing apparatus entered the tunnel to tackle the fire.
“”The incident is still causing significant disruption in central London, with multiple road closures and a safety cordon currently in place.
“Several bus routes have been diverted, and the public are advised to continue to avoid the area where possible.”
The fire was brought under control by 2.07pm, but crews remain on site, and a safety cordon is in place.
The Brigade’s Fire Investigation team is now working to establish the cause.
No injuries have been reported.
Crews from Soho, Euston, Shoreditch, Islington, Lambeth and surrounding fire stations were dispatched to the scene.
