(CNN) -- An Iowa community was shut down much of Sunday afternoon while emergency crews remained hard at work, sifting through wreckage caused by a wave of powerful tornadoes that swept across the state overnight.
The twisters caused major damage to about 60% of Mapleton, a city of about 1,200 residents, Monona County Sheriff Jeff Pratt told reporters Sunday.
It was all part of a violent storm system that struck overnight, originating in eastern Nebraska and following a warm front across northern Iowa, according to National Weather Service meteorologist Frank Boksa.
But despite causing extensive damage, it did not lead to any fatalities, said Stefanie Bond, a spokeswoman for Iowa's Homeland Security & Emergency Management Division.
Mapleton was among the hardest-hit areas. Initially, concerns about a gas leak had prompted all nonresidents to be barred from the community, which is about 45 miles southeast of Sioux City. By 5 p.m., people were being allowed back in, though authorities remained on the scene, according to the sheriff's department.
The high winds tossed cars and tractors, tore off roofs, caused a car wash to collapse, uprooted trees and downed power lines. Yet Pratt said there had been only minor injuries, giving credit to advance warning as well as an emergency response effort that included authorities both local and from elsewhere.
"There was major devastation to the southwest portion of town, but no fatalities," the sheriff said.
Iowa Gov. Terry E. Branstad issued a disaster proclamation for Monona County, according to a statement from his office. The proclamation allows officials to use state funds to help. He later issued a similar proclamation for Pocahontas County, which also suffered severe damage.
He then toured the tornado-ravaged town on Sunday afternoon, posting pictures online of uprooted trees and conversations with residents. On his Twitter page, Branstad wrote, "Please keep the victims in your thoughts and prayers."
The twisters struck just before midnight Saturday.
Amateur video recorded by storm chasers shows a large funnel cloud spinning across a flat terrain outside Mapleton.
In the background, a passenger can be heard exclaiming, "It's going to hit that town! ... Mapleton's in big trouble!"
Afterward, National Guard troops were brought into the area, according to Stefanie Bond, a public information officer for the state's Homeland Security & Emergency Management Division. She also said that natural gas service was temporarily shut off in the city.
The Red Cross was also on the ground providing assistance. Bruce Spence, a government liaison for the group, called the damage to the town "extensive."
"The whole town is without power. Main Street is a disaster," he told CNN. "They've shut down the town. As we speak, I'm looking down one of the residential streets. There's debris all over, trees are down.
"This isn't going to get fixed soon," Spence said.
The National Weather Service in Des Moines, Iowa, reported tornado sightings by storm chasers and trained spotters in as many as 11 towns and cities in northern and west-central Iowa over a four-hour period Saturday night.
At least three of the twisters, including the Mapleton tornado, caused significant damage, according to Boksa.
In Early, a town of 1,600 residents, a tornado ripped roofs off buildings and homes and uprooted large trees, authorities said. There were no reports of injuries in that town. In Schaller, a twister knocked down a dozen trees and felled multiple power poles, the weather service reported.
Tammie Pech, a Red Cross spokeswoman, said the agency was opening shelters in Mapleton and Early to take in storm victims. Only four people slept in the Mapleton shelter overnight Sunday, Spence said. Most displaced residents opted to stay with family and friends, he said.
The National Weather Service also reported major damage in Nemaha, possibly from a tornado.
Bond noted that strong winds also tore through hog pens in Pocohontas Country, in central Iowa, and Kossuth County, in the east along the Illinois border.
Three cities in Fayette County -- Fayette, Westgate and Maynard -- were without power for about an hour Sunday evening due to a blown transformer, the state's emergency management spokeswoman said.
Randy Frank, Fayette County's homeland security and emergency management coordinator, said that the challenges continued well after the tornadoes came through, with sustained winds blowing at least 50 mph into Sunday evening.
"Our biggest problem right now is fuel fires out of control," said Frank, whose county is about 255 miles from Monona County. "And it's that way across the state, with the wind, which (can) be very dangerous in (fanning) the fire."
CNN's Greg Morrison, Greg Botelho and Leslie Tripp contributed to this report.