Washington DC - Much of the eastern US was lashed by intense storms Monday, leaving at least two people dead, hundreds of thousands without power and thousands of flights canceled or delayed.

Millions of people were under severe weather alerts, including tornado watches, as rain, strong winds and hail swept east along nearly the entire eastern seaboard, from Alabama to New York.

The National Weather Service (NWS) had predicted a "moderate risk" of hazardous storms, with gusts up to 80 miles per hour.

"Stay weather aware and make sure you have multiple ways to receive warnings," the NWS in Baltimore and Washington said on social media earlier in the day.

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As much of the severe weather danger subsided into the late evening, some areas faced flood threats as rain continued to fall.

The NWS issued flash flood warnings for Washington and the cities of Arlington and Alexandria in neighboring Virginia until 2:45 AM EDT Tuesday.

Hail as large as 4.5 inches in diameter was recorded in Virginia, the NWS said.

In Alabama, a 28-year-old man died after being struck by lightning in an industrial park parking lot, a local ABC station reported.

And in South Carolina, a 15-year-old was killed when he was hit by a falling tree outside his grandparents' house, according to a local CBS station.

By early Tuesday, nearly 600,000 customers were without power along the East Coast, from Pennsylvania to Georgia, according to tracking website PowerOutage.us.

Local media and government agencies in Maryland released images of downed power lines strewn across streets, and trees that fell into homes and across roads and rail lines.

Other southern states experienced similar storm damage, with Georgia Power releasing photos of fallen trees that pulled down power lines due to high winds, hail, and heavy rain.

"Our crews are working safely and as quickly as possible to get the lights back on," the electric utility said on X, formerly known as Twitter.

More than 1,700 US flights were canceled on Monday and more than 8,000 delayed as the severe weather loomed, website FlightAware said.

In Washington DC, federal agencies sent employees home early at 3:00 PM Monday in anticipation of the weather.

The storms came as large parts of the southern US, including Texas, Louisiana, and Florida boiled under excessive heat warnings, with temperatures up to 108 degrees Fahrenheit predicted through Tuesday. Out-of-control wildfires are also raging in California.

Scientists say climate change has amplified the intensity and frequency of extreme weather events around the world.