By Miguel Llanos and Jim Gold, msnbc.com staff
Updated at 4:45 p.m. ET: At least two tornadoes touched down in areas south of Dallas on Tuesday, causing widespread damage. The National Weather Service described them as "large and extremely dangerous" as the storm system moved northeast and later spawned another tornado in Forney, a suburb just east of Dallas, where a school was hit a few minutes ago, NBC News reported.
With the storms still moving through the region, many properties were damaged or destroyed and the Dallas Fort-Worth International Airport was hit by large hail, NBCDFW.com reported.
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Dallas flights were shut down and travelers were taken to shelters as the storms passed. American Airlines canceled nearly all its remaining flights Tuesday due to potential hail damage to aircraft.
One tornado hit the Flying J Truck Plaza in Dallas, tossing two trucks, said driver Michael Glennon, who caught the destruction on his video camera.
"The second trailer is ripped to pieces and thrown 50 to 100 feet into the air," Reuters quoted him as saying.
"This is a serious situation," the NBC affiliate reported over the air at the height of the storms, as meteorologists showed live footage of "debris balls" in Dallas, Ellis, Johnson and Tarrant counties, where officials were trying to get a tally of injuries and damage.
Live video showed a huge funnel cloud moving through a populated area as flashes of exploding power lines lit the sky. Vehicles were thrown across a major highway.
Large trucks were seen being flung through the air. "There's lots of 18-wheelers," said one NBC 5 reporter near Arlington. "I've never seen this before."
Arlington's mayor declared a state of emergency, and many homes there were destroyed or damaged, NBC 5's Mola Lenghi reported. A local nursing home was hit hard, with one person hospitalized.
In Lancaster, NBC 5 reporter Ken Kalthoff said "there's tremendous damage here." More than 100 children and adults inside a daycare center there appeared safe but the building was heavily damaged.
No deaths were reported but an undetermined number of people were injured, he added. Tornado sirens went off ahead of the touchdown.
"People have stumbled out of their houses surprised they survived,"reported Kalthoff, who saw the funnel cloud about a mile away.
The Lancaster high school and a large water tank barely avoided damage, he added.
Downtown Dallas was not in the eye of the funnel clouds, but the areas south of the city are also heavily populated.
"Considerable damage" was also reported near Cleburne, a city of 30,000 some 30 miles south of Fort Worth, the National Weather Service said.
The storms started near Cleburne, but most of the damage was to the north toward Dallas, city spokesman Charlie Hodges told msnbc.com.
Schools south of Dallas were locked down, NBC's Charles Hadlock reported, adding that one of the funnel clouds touched down in the town of Red Oak.
At least 35,000 customers lost power in the storms, which also dumped hail the size of golf balls across the area.
Mobile homes and businesses were destroyed or damaged in Kennedale and one person was hospitalized, the fire department said.
The massive Parks at Arlington mall along Interstate 20 shut down and management ordered shoppers and others into the basement, the Fort Worth Star-Telegram reported.
Employees at Cowboys Stadium in Arlington were moved into the tunnels, the newspaper said.
At DFW Airport, American Airlines was having to inspect 68 planes for hail damage. Thirty-seven American flights were diverted and will stay in those cities overnight.
American Eagle Airlines, the world's largest regional airline, diverted 11 flights, and 33 of its planes will be inspected.
The Associated Press and Reuters contributed to this report.