BUENOS AIRES, Argentina—A power outage hit most of Argentina's capital and caused severe traffic jams during rush hour.

Officials say Wednesday evening's blackout affected more than a million homes, paralyzed the subway system and put more than 1,000 traffic lights out of action on major avenues as people headed home after work.

Power also failed at Argentina's Congress and the presidential Pink Palace but was restored. Electricity resumed in most of the city within two hours, but some neighborhoods remained in the dark hours later.

The Edesur energy company says the outage was caused by a failure in two high voltage lines. The outage comes after three days of extreme heat that caused record-high demand for electricity that has put a strain on the energy grid.