Workers were racing to restore power in the area around Sukhumvit Soi 31 on Saturday afternoon after a tangle of overhead cables caught fire.
The fire occurred in front of Sawasdee Wittaya School, about 700 metres into Soi 31 off Sukhumvit Road in Watthana district, according to JS100 traffic radio.
Firefighters and rescue workers rushed to the area to control the blaze, believed to have been caused by an electrical short circuit, Thai media reported.
The Metropolitan Electricity Authority tweeted that the agency had been alerted about the blackout and had sent repair crews to the area.