Strong thunderstorms toppled trees and power lines across north Alabama on Friday, damaging homes and businesses and prompting schools to dismiss thousands of students early as a precaution.

No injuries were reported, but forecasters said tornadoes would be a threat for hours.

Systems throughout the Birmingham metropolitan area dismissed students ahead of a wave of storms as reports of scattered damage came in from across north Alabama, where powerful winds battered several counties earlier.

Falling trees struck several houses and a nursing home in Cullman, and authorities ordered an evacuation of everyone within a half-mile radius of a downtown area where a gas leak was reported. Power was out throughout town.

"It came up on us so quickly. Everything happened at once," said Leanne Collins, who works at City Hall.

Damage also was reported in the Tennessee Valley in Madison, Colbert and Limestone counties, with winds gusting to more than 40 mph in Tuscumbia. Several barns, a small manufacturing plant and a handful of homes were hit.

Authorities said it appeared the damage was caused by straight-line winds instead of a tornado.

"We were very lucky. We did not have anyone report seeing a tornado, but we were under a warning," said Daphne Ellison of the Limestone County Emergency Management Agency.

In Colbert County, emergency management director Mike Melton said power lines and trees were down in a wide area.

"There's about a four-mile path of damage," he said.

The weather forced officials to halt the search on the Tennessee River for the body of a woman who has been missing since a barge collided with a pleasure boat on March 27, Melton said. Three other bodies already have been located.

The weather service issued a tornado watch for 21 counties in central Alabama.

The storms are part of a weather system that hit Arkansas on Thursday, knocking out power to thousands and causing widespread damage.