Millions of Americans sweated through a scorching weekend as temperatures soared across the U.S., while residents were rescued from floodwaters that forced evacuations across the Midwest. One person was killed during flooding in South Dakota, the governor said.

From the mid-Atlantic to Maine, across the Great Lakes region, and throughout the West to California, public officials cautioned residents about the dangers of excessive heat and humidity.

At the borders of South Dakota, Iowa and Minnesota, floodwaters rose over several days. In northwest Iowa, 13 rivers flooded the area, said Eric Tigges of Clay County emergency management. Entire neighborhoods — and at least one entire town — were evacuated, and the Iowa town of Spencer imposed a curfew Sunday for the second night in a row after flooding that surpassed the record set in 1953.

“When the flood gauge is underwater, it’s really high,” Tigges said at a news conference organized by Spencer officials.

Gov. Kim Reynolds declared a disaster for 21 counties in northern Iowa, including Sioux County. In drone video posted by the local sheriff, no streets were visible, just roofs and treetops poking above the water.

National Guard troops were helping with water rescues and transporting needed medications lost in flooding.

“Businesses are shuttered. Main streets have been impacted,” Reynolds said. “Hospitals, nursing homes and other care facilities were evacuated. Cities are without power, and some are without drinkable water.”

National Weather Service meteorologist Donna Dubberke said parts of northern Nebraska, southeastern South Dakota, southern Minnesota and northwest Iowa received eight times the typical average rainfall. And more heavy rain was expected this week.

In South Dakota, Gov. Kristi Noem declared an emergency after severe flooding in the southeastern part. Several highways were closed.

Areas south of Sioux Falls, the state’s largest city, had an estimated 10 to 15 inches (25 to 38 centimeters) of rain over three days, National Weather Service hydrologist Kevin Low said.

At least one person died in the floods, Noem said Sunday, without providing details.

Several rivers, including the Big Sioux, James and Vermillion, were expected to peak sometime Monday through Wednesday night, the governor said at a news conference.

“I want to remind everybody to remember the power of water and the flow of water, and to stay away from flooded areas,” Noem said. “We’ve got a few days in front of us here that’ll be a little rough, but we’ll get through it.”

Emergency management officials in the small South Dakota community of Dakota Dunes on Sunday issued a voluntary evacuation order for the area’s roughly 4,000 residents. Dakota Dunes is near the Nebraska and Iowa borders and is sandwiched between the Missouri and Big Sioux rivers, both of which are expected to crest in the coming days. Emergency management in Dakota Dunes warned residents that a mandatory evacuation could come quickly if flood barriers are breached.

Minor to moderate flooding was expected along the Missouri River, according to officials with the U.S. Army Corps of Engineers.

“As long as the levees hold, we’re not expecting any major impacts,” said John Remus, water management division chief for the corps in the Missouri River basin.

But elsewhere, the heat was the biggest worry.

“It’s more important for people who are going to be outside to stay hydrated, because heat, humidity and low winds, even if you’re in good shape and not really acclimated to it, it could be a danger,” said Bruce Thoren, a National Weather Service meteorologist in Oklahoma. “It happens quickly.”

The cities of Washington, D.C., Baltimore and Philadelphia all saw record heat on over the weekend.

Last year the U.S. experienced the most heat waves since 1936, experts said. An AP analysis of data from the Centers for Disease Control and Prevention found that excessive heat contributed to more than 2,300 deaths, the highest in 45 years of records.

The National Weather Service warned of the potential for rare tornadoes in the Northeast later Sunday. Tornadoes on Saturday struck in Wisconsin, leveling the historic Apple Grove Lutheran Church, founded in 1893 in the town of Argyle.

“The good news is we are all safe,” Dan Bohlman, pastor of Apple Grove Lutheran, said on the church website.

Marvin Boyd, meteorologist at the National Weather Service in Burlington, Vermont, said a severe thunderstorm warning was issued for parts of northern New York as a storm with wind gusts exceeding 60 mph (95 kph) and the threat of tornadoes head toward Vermont near Lake Champlain. It was one of several expected to pass through the region Sunday afternoon.

“It’s an unusual alignment of ingredients for Vermont and northern New York to produce a threat of tornadoes,” Boyd said.

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Associated Press journalists Summer Ballentine in Columbia, Missouri; Leah Willingham in Charleston, West Virginia; Julie Walker in New York; Ron Todt in Philadelphia; and Michael Casey in Boston contributed reporting.