PARKERSBURG, Iowa — Half of this small town lay in ruins or heavily damaged Monday following a deadly tornado that ripped apart a stretch of northern Iowa.

The Sunday afternoon twister killed six people in Iowa, four of them in Parkersburg and two others in nearby New Hartford. In neighboring Minnesota, a child was killed by violent weather in a suburb of St. Paul.

"You really are overwhelmed when you see it," Iowa Gov. Chet Culver said at a news conference Monday after touring the Parkersburg area. "You can't imagine this kind of devastation, homes completely gone. And to see people trying to sort through their belongings is very difficult."

Rescuers continued picking through the wreckage in search of possible victims but officials said they were hopeful that no one else remained to be found.

In addition to those killed, about 70 people were injured, two of them in critical condition.

Officials counted 222 homes destroyed, 21 businesses destroyed and more than 400 homes damaged. Among the buildings destroyed were city hall, the high school and the town's sole grocery store and gas station.

That's about half of the homes in Parkersburg destroyed or severely damaged, said Butler County Sheriff Jason Johnson.

"There's so much hurt here, I don't know where to start," said U.S. Sen. Chuck Grassley, who owns a farm near New Hartford.

Warning sirens sounded early enough to give residents time to seek shelter, said Parkersburg Mayor Bob Haylock.

"Without that, we would have a tremendous amount of injuries and loss of life," Haylock said. "People were down in their basements and waiting it out."

However, Haylock said most of those killed in Parkersburg were in basements. All were adults, he said.

Diane Goodrich rode out the storm in her basement with her husband and three neighbors.

"The noise was just unbelievable," Goodrich said Monday as she searched through the ruins of her home. "Our ears were popping. We could hear trees flying over us. We could hear every piece of furniture that left the house."

The number killed initially was reported as seven but was dropped to six Monday after a better accounting of residents, said Bret Voorhees, bureau chief of Iowa Homeland Security and Emergency Management.

The storm struck just after 5 p.m. Sunday, following an east-to-west path just a few miles north of the Waterloo area. It hit Parkersburg, New Hartford and then Dunkerton, about 50 miles east of Parkersburg. About 80 miles to the southwest, the Des Moines area had heavy rain and wind that gusted to 70 mph.

Iowa Gov. Chet Culver issued a disaster proclamation for Black Hawk, Buchanan and Butler counties.

North of St. Paul, Minn., a violent storm struck the town of Hugo, killing a 2-year-old boy and critically injuring his young sister, officials said. The children's parents also were hospitalized, as were three other adults and another child.

Hugo resident Marvin Miller found the 2-year-old boy's parents, his neigbors, trapped in the debris of their home.

"They just kept screaming, 'My children, my children!' Miller said Monday.

Washington County, Minn., Sheriff Bill Hutton said Monday that 40 to 50 homes were uninhabitable in Hugo and 150 to 200 others were damaged to some extent.

Hugo Public Works Director Chris Petree said his family took shelter in their basement, huddling against a foundation wall, before the storm lifted his house off the ground and completely wiped out the second floor.

"All you hear is glass breaking and wood tearing and breaking in half," Petree said.

The storms came after three days of violent weather elsewhere across the nation. Rural Oklahoma was battered Saturday and storms in Kansas a day earlier killed at least two people.

About 100 people have been killed by U.S. twisters so far this year, the worst toll in a decade, according to the weather service, and the danger has not passed yet. Tornado season typically peaks in the spring and early summer, then again in the late fall.

Associated Press writer Joshua Freed in Hugo, Minn., contributed to this report.