Fire crews are tackling a fire at an electricity sub station in Brentford.
The blaze is thought to have started at a sub station in Catherine Wheel Road sometime after 10am.
Shops and businesses reported intermittent cuts in power at about 9am.
Shortly after 10am there was another power cut.
About a dozen businesses are without electricity and some, including NatWest and the post office, have closed.
A spokesman for the London Fire Brigade said: "The electricity board has gone to the site and isolated the supply.
"Crews remain on standby."
Catherine Wheel Road is closed to traffic and diversions are in place.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here