Some 22,000 Pepco customers in D.C. and Prince George’s County were thrust into darkness Friday morning after a falling tree severed a transmission line, a spokesman for the power utility says.

The outages were first reported by frustrated Pepco customers on Twitter shortly after 11:30 a.m., although the Pepco spokesman, Bob Hainey, cannot specify exactly when the line came down. The damage to the transmission line is affecting four substations serving southern Prince George’s County and a large portion of the District.

Currently, 18,000 Pepco customers in Prince George’s County are without power, while another 4,000 in D.C. are sitting in the dark. The affected customers in the District appear to be largely concentrated in wards 5, 6, 7, and 8. The affected areas can be viewed on Pepco’s outage map.

Hainey says Pepco crews have been dispatched to the downed transmission line and are aiming to restore power to most of the affected areas within an hour.