WASHINGTON — At least two tornadoes ripped across northern Texas Tuesday, flipping huge trucks like toys, tearing off roofs and grounding flights but apparently causing only minor casualties.

One twister touched down in a parking lot full of tractor-trailers -- large trucks that move shipping-container sized cargos, and television images showed several containers twisting and flying dozens of feet up into the air.

"It was raining and hailing like I said... and then all of a sudden, the rain and hail ceased... that's when we saw the tornadoes touch down," witness Jonathan Cook told CNN.

The resident of Burleson said he dashed out of the bank when he saw hail the size of nickel coins start falling and leapt back into his truck to get it to the cover of a nearby gas station.

"We were just under the gas pump awning, hoping it didn't come our way. We had a good visual of it, but we really had nowhere to go... we just had to run in the gas station."

Texas residents appeared mostly to have heeded warnings as the National Weather Service sent out an alert saying "Tornado Emergency. Two tornadoes are currently affecting the DFW (Dallas-Fort Worth) Metroplex. Take cover now!"

A tornado watch was issued for the Dallas-Fort Worth area -- home to more than six million people -- until 8:00 pm (0100 GMT Wednesday).

On his drive home Cook said "there were large trees, large tree limbs, a lot of leaves scattered across the highway, and tree limbs on the highway," as well as "many roofs taken off homes."

The tornadoes caused major damage in several metropolitan areas, including Kennedale, Arlington and Lancaster, local media reported.

The area utility company, Oncor, reported hundreds of outages affecting tens of thousands of customers in the metro area. Dallas police warned residents to stay away from dangling power cables.

But despite the powerful storm, casualties appeared to be minimal.

"At this point, there are no major injuries reported," Arlington Mayor Robert Cluck said in a statement.

"However, it is still early" and city fire and police units "are assessing damages to buildings, homes, and vehicles primarily in the southern part of the city."

David Magana, a spokesman for the busy Dallas-Fort Worth airport, told CNN that federal authorities had issued a ground stop, meaning all flights headed to Dallas had been held on the ground at their airports of origin.

Airport passengers were sheltering at the huge facility, though flights were expected to soon resume, Magana said.

The airport is the main hub for American Airlines and its regional carrier, American Eagle. American announced on its Twitter feed that "due to severe weather," all of its airport operations "are canceled through this evening."

The DFW airport authority however said via Twitter that it was still in operation. "NO RISK. We are staying open," the message read.

"We've activated our Irregular Operations Plan. Restaurants will stay open to accommodate passengers whose flights are delayed or canceled," DFW officials added in a separate Twitter message.

American Airlines said it was conducting a "top-to-bottom" check of all their airplanes searching for dents and damage.

"I do not know of any significant damage at the airport," the airlines spokesman Tim Smith told Fox News. "We'll get things up and running fast as we can."

Lieutenant Governor David Dewhurst warned Texans to be prepared that more bad weather could come.

"We're in the tornado season, so please ladies and gentlemen, pay attention and if there are any warnings ... go inside room, ground floor and be safe, please," he said.

[Tornado image via Shutterstock]