A power cut has struck London Road in Brighton after a small fire at the substation beneath Preston Circus Fire Station.
The substation, operated by UK Power Networks, has been dealt with by firefighters, but all traffic lights and signalling systems at the Preston Circus junction are currently inactive.
The East Sussex Fire and Rescue Service has confirmed police have been called and are on the scene directing traffic.
A spokeswoman for UK Power Networks said: "UK Power Networks engineers are working to restore electricity supplies in the Viaduct Road area of Preston Circus, Brighton.
"For safety reasons we needed to isolate supplies to 669 customers at 6.37pm this evening after a fault on a piece of equipment at a local substation.
"We are sorry for any inconvenience this is causing. Our engineers are working hard at the scene to reconnect supplies as swiftly as possible."