A storm system spawned tornados as it swept across the upper Midwest and into Pennsylvania, killing at least one person, flooding basements and leaving thousands of homes and businesses without power early Friday.

In western Pennsylvania, Allegheny County and Pittsburgh officials declared a state of emergency as residents dealt with flooding and damage from the torrential downpours.

The worst damage in Ohio was across the north-central part of the state, where the National Weather Service confirmed a tornado in Shelby and were investigating tornado reports in several counties, meteorologist Walter Fitzgerald said.

©Richelle via WKYC
NBC affiliate WKYC obtained this storm photograph from a viewer who said it was taken over Richland County, Ohio, on Thursday. The formation is known as a supercell, a well organized and notably intense thunderstorm.

The storms tore parts of the roofs off a high school and a factory, damaged several other buildings, and downed trees across a swath of the state.

In Marion, about 40 miles north of Columbus, a falling tree limb struck a sport utility vehicle, killing 22-year-old Shawna Stevens a few blocks from her home, police said.

"About half the city is without power, and we have a lot of cleaning up to do in the next few days," Lt. Michael Shade said.

Tens of thousands of utility customers throughout the storm region lost power at the height of the rain and wind.

Witnesses reported that the tornado in Shelby a plant that makes steel pipe and tubular products, Mayor Jim Henkel said. The roof was damaged and some walls were blown down, but there were no reports of injuries.

Power lines were down in Shelby, and the tornado moved cars in the parking lot and blew out car windows, the mayor said. In nearby Ashland County, the roof of Black River High School was blown off, according to sheriff's Capt. Terry Hamilton.

Wind also damaged a restaurant and blew out car windows in a supermarket parking lot in Salem, about 15 miles southwest of Youngstown.

In western Pennsylvania, emergency dispatchers said they received several reports of funnel clouds, and about 35,000 homes and businesses were without electricity Friday morning. Duquesne Light spokesman Joe Vallarian said some customers might not have service until Saturday, because of heavy damage to power lines

The storm shattered windows at Pittsburgh's Carnegie Science Center with 800 to 1,000 people inside. About two dozen people in the city were treated for minor injuries, authorities said.

The town of Millvale, on the outskirts of Pittsburgh, was hit hard by flooding: 25 of about 200 flooded homes had water up to the first floor, county Executive Dan Onorato said. Forty-five businesses also flooded. The same town had been badly damaged when the remnants of Hurricane Ivan cause a creek to overflow in 2004.

Hundreds of passengers at Philadelphia International Airport were stuck on planes that sat on runways for hours Thursday. US Airways said it canceled 530 flights across the country Thursday, 133 of them out of Philadelphia.

The airline said bad weather elsewhere created a backlog of planes waiting to takeoff, stranding some passengers on the tarmac for up to six hours. Nearly 30 planes were lined up at one point Thursday.