US government offices in the Washington D.C. area closed early on Monday because of threatening weather as forecasters warned people across the eastern US of possible tornadoes, damaging winds and large hailstones.

Fast-moving thunderstorms and powerful winds toppled trees and knocked out power for nearly 200,000 homes and businesses in neighbouring Maryland and Virginia, according to tracking website PowerOutage.us. As many as 800,000 customers had lost power in the southern and mid-Atlantic states.

Though drenched with rain and pelted with some hail, the nation’s capital had escaped any twisters by the time a National Weather Service tornado watch expired at 9pm EDT (01:00 GMT).

A coastal flood advisory remained in effect for Washington until 4am (08:000 GMT).

The National Weather Service said more than 29.5 million people from Alabama to western New York state had been at risk of tornadoes on Monday, but none had been reported as of 9pm EDT.

The Federal Aviation Administration ordered departing flights grounded at airports in New York, Washington, Philadelphia, Atlanta and Baltimore because of thunderstorms. The FAA said it was rerouting aircraft around the storms as much as possible.

Libraries, museums, the National Zoo, pools and other municipal and federal services in the Washington area were also closing early. The US Office of Personnel Management said federal employees had to depart no later than 3pm

FlightAware, a flight tracking site, said more than 2,600 US flights had been cancelled, including 102 at Washington Reagan National Airport and 35 at Washington Dulles. Another 7,700 US flights had been delayed.