Tornadoes that ripped through the central United States have killed six people, including four teenagers at a Boy Scout camp.

Officials in the central state of Iowa say the four teenagers were killed and more than 40 other people injured when a tornado smashed into their campsite Little Sioux Scout Ranch in the western part of the state Wednesday.

U.S. Homeland Security Secretary Michael Chertoff toured the site Thursday, calling the deadly storm system a "tragic act of God."

In Rome today, a White House spokeswoman said President George Bush was saddened to hear about the deaths of the teenagers and sends his condolences to their families.

Witnesses say the tornado struck so quickly there was little time to react.

Two other people were killed when tornadoes swept through the central state of Kansas.

Weather forecasters say, in all, about 30 tornadoes touched down across the region.

Meanwhile, other parts of the central U.S have been hit by severe flooding. Areas along the Mississippi River have been evacuated as more storms threaten to push the river and its tributaries over their banks.

Iowa Governor Chet Culver, speaking at the news conference with Secretary Chertoff, said that almost every river in the state was in danger of flooding.

Chertoff called the tornadoes and flooding a remarkable onslaught of weather. He said the government is working closely with local officials, and trying to make sure resources will be available if and when more storms hit.

The U.S. National Weather Service says this could be the worst flooding to hit the central U.S. in 15 years. Officials say floods have already caused hundreds of millions of dollars worth of damage.

Elsewhere, firefighters in the western state of California are battling wildfires that have burned more than three square kilometers and forced hundreds of residents to flee their homes.