Five people died and at least 35 were hurt as powerful tornadoes ripped through the US state of Iowa on Tuesday, with one carving a path of destruction through the town of Greenfield, according to state officials.

The extreme weather also ripped apart and crumpled massive power-producing wind turbines several kilometres outside the town.

The Iowa Department of Public Safety said on Wednesday, local time, that four people had been killed in the area, but did not release their names because relatives were still being notified.

It brought the total number of deaths to five, after authorities previously announced that a woman in a vehicle had been killed by a tornado about 40km from the town.

The Greenfield tornado left a wide trail of obliterated homes, splintered trees and crumpled cars throughout the town, which sits about 88.5km south-west of Des Moines and is home to 2,000 people.

Greenfield resident Kimberly Ergish, 33, and her husband on Wednesday dug through the debris field that used to be their home, looking for family photos and other salvageable items.

There wasn't much left, she acknowledged.

The reality of having her house destroyed in seconds hadn't really set in, she said.

"If it weren't for all the bumps and bruises and the achy bones, I would think that it didn't happen," she said.

Forecasters' worst-case scenario

The National Weather Service said initial surveys indicated at least an EF-3 tornado had hit Greenfield, but additional damage assessment could lead to a more powerful ranking.

It appeared to have been on the ground for more than 64km, AccuWeather chief meteorologist Jon Porter said, bringing to life a worst-case scenario that weather forecasters had long feared.

"Debris was lifted thousands of feet in the air and ended up falling to the ground several counties away from Greenfield. That's evidence of just how intense and deadly this tornado was," he said.

A satellite photo taken by a BlackSky Technology shows where the tornado gouged a nearly straight path of destruction through the town, just south of Greenfield's centre square.

Greenfield's 25-bed hospital was among the buildings damaged, and at least a dozen people who were hurt had to be taken to facilities elsewhere.

Residential streets that on Monday were lined with old-growth trees became a chaotic jumble of splintered and smashed remnants by Wednesday.

Many of the homes' basements where residents had sheltered lay exposed, and front yards were littered with belongings from furniture to children's toys and Christmas decorations.

People as far as 160km away from Greenfield posted photos on Facebook of ripped family photos, yearbook pages and other items that were lifted into the sky by the tornado.

About 144km away, in Ames, Iowa, Nicole Banner found a yellowed page declaring "This Book is the Property of the Greenfield Community School District" stuck to her garage door like a Post-It note after the storm passed.

"We just couldn't believe it had travelled that far," she said.

White House press secretary Karine Jean-Pierre said FEMA's administrator would head to Iowa on Thursday and that the White House was in touch with state and local officials.

She said they were "praying for those who tragically lost their lives" and wished those injured a "speedy recovery".

Wind turbines crumpled, burnt

A wind farm in south-west Iowa suffered a direct hit from the powerful tornado near Greenfield, which crumpled five of the massive, power-producing towers, including one that burst into flames.

Video of the direct hit on the wind farm near Greenfield, Iowa, showed frightening images of the violent twister ripping through the countryside, uprooting trees, damaging buildings and sending dirt and debris high into the air.

Several of the turbines at MidAmerican Energy Company's Orient wind farm recorded wind speeds of more than 160 kilometres per hour as the tornadoes approached, just before they were destroyed, the company said in a statement.

"This was an unprecedented impact on our wind fleet, and we have operated wind farms since 2004," MidAmerican said.

While there have been isolated incidents of tornadoes or hurricanes damaging wind turbines, fortunately such occurrences are extremely rare, said Jason Ryan, a spokesperson for the American Clean Power Association.

Although requirements vary from state to state about how far turbines must be located from other structures, he said giant turbines are never placed directly next to homes or other occupied structures.

There are currently nearly 73,000 wind turbines in operation across the US, he said. Many of those operate in the centre of the country, often referred to as the wind belt, which stretches from Texas north through Oklahoma, Kansas, Nebraska and the Dakotas, and includes large parts of Minnesota, Iowa and Illinois.

Wind turbines are built to withstand high wind speeds and severe weather, like tornadoes, hurricanes and lightning strikes, but few structures are designed to withstand a direct hit from a powerful tornado, said Sri Sritharan, an engineering professor at Iowa State University.

Climate change heightens storm severity

Storms also pummelled parts of Illinois and Wisconsin on Tuesday, knocking out power to tens of thousands of customers in the two states.