CONCORD, N.H. -- Powerful thunderstorms sparked tornado warnings and flood warnings, caused building collapses and have been blamed for one death Thursday afternoon, reported WMUR-TV in Manchester, N.H.

Gov. John Lynch declared a state of emergency in Merrimack, Strafford, Belknap, Carroll and Rockingham counties and called out the National Guard to help after the storms cross New Hampshire.

"It appears that there are at least 100 homes damaged and probably at least a half-dozen homes which have been completely destroyed," Lynch said after a helicopter tour.

"It was a narrow swath of destruction that went from Epsom all the way to New Durham," he said.

Police and firefighters were going door to door in the storm-ravaged areas, which stretched from about 10 miles east of Concord to beyond the eastern end of Lake Winnipesaukee near the Maine border.

Downed trees and power lines blocked many roads, delaying emergency responders.

The storm knocked out power to 6,000 homes and businesses.

Some witnesses described seeing a funnel cloud or clouds in the storms, and the National Weather Service issued a tornado warning just before noon.

Reports also came in of people trapped in cars in Alton and multiple building collapses in Barnstead. Ambulances responded from as far away as Belmont to assist in Barnstead, and a viewer reported that North Barnstead Road was impassable.

A flood watch was issued for Strafford County in New Hampshire and York County in Maine. The National Weather Service reported a storm moving from Exeter to Dover to Sanford.

The warning means flooding has been reported or is imminent. Rainfall of more than an inch an hour was expected, which could flood small streams and cause ponding on streets.

Safety and environmental officials said they were most concerned about flooding along the Pemigewasset, Contoocook and Baker rivers.

"We are particularly concerned about public safety because people do not normally expect flooding this time of year," said Christopher M. Pope, director of Homeland Security and Emergency Management. "We also have many out-of-state visitors, people in campgrounds and others enjoying the outdoors. We don't want them to be taken by surprise by sudden flooding."

The National Weather Service predicted minor flooding of the Pemigewasset at Woodstock, Plymouth and Rumney, with water a foot or a foot and a half above flood stage. Levels could reach flood stage on the Contoocook River at Henniker, the Warner River at Davisville and the Baker River at Bristol.

Pope said residents and visitors should watch out for sudden rises in river levels and heed flood watches or warnings. He also said driving on roadways covered with water is dangerous because the road surface may have been washed away.

Skarupa said the storms are expected to taper off late Thursday. Friday is expected to be clear.