As many as 10 tornadoes may have been spotted in North Texas on Tuesday, damaging homes and businesses in Arlington, Kennedale and Lancaster, knocking out power to tens of thousands and forcing American Airlines to cancel more than 450 flights, officials said.Preliminary estimates are that six to 10 tornadoes were reported, the National Weather Service said.The havoc began shortly after lunch, as radar lighted up with reports of large hail, high winds and possible tornadic activity from Parker County into southern Dallas County.There were no initial reports of major injuries or deaths from the storms, but trees were uprooted and blown onto vehicles, roofs were torn off buildings and wood and brick debris littered neighborhoods. Two people were reportedly hurt in Arlington.DFW Airport recorded 1.43 inches of rain.Homes along Green Oaks Boulevard north and south of Interstate 20 appeared to be hit the hardest in Arlington, with residents reporting missing roofs, broken windows, flooded homes, downed trees and damaged vehicles.Arlington Mayor Robert Cluck declared a state of emergency, paving the way for state and federal aid.Arlington police said late Tuesday that about 150 homes were damaged and that about 12,600 residents were without power. About 40,000 were without power throughout the region, according to Oncor Electric Delivery.The worst damage in Arlington, police said, included:-- Green Oaks Nursing Home and Rehabilitation Center, 3000 block of West Green Oaks Boulevard, which sustained heavy damage, including a collapsed roof. One person suffered minor injuries. The center was evacuated, and about 35 residents were moved to other nursing homes.-- Two buildings at the Chesterfield Apartments in the 5700 block of Median Way were severely damaged. Vehicles were overturned and the roof was damaged. In a nearby neighborhood close to U.S. 287, 25 to 30 homes were damaged.-- One person was injured and about 100 homes were damaged in the Oldfield neighborhood, just south of the 4500 block of West Pleasant Ridge Road.-- Structural and roof damage reports continued to come in, mostly in southwest Arlington and along I-20 and Cooper Street.The Salvation Army dispatched a mobile kitchen for residents in Kennedale, and another to assist residents in Pleasant Grove.Kennedale schools associate superintendent Rick Edwards said that the tornado did "a lot of damage in Kennedale," but that the students and schools were OK.He said he watched the storm as it bore down on the town. "We were very fortunate. When we heard the first report at Burleson we went into duck-and-cover mode. There's been no damage to any of our buildings. "We saw the tornado, it went right up between Patterson Elementary and the high school buildings, but it went right between them. I saw it. It passed about a mile from our office here."Sen. John Cornyn issued a statement saying anyone who needs assistance should contact his office at 972-239-1310 or online at http://www.cornyn.senate.gov/public/index.cfm?p=ContactForm.Several residents reported ruptured gas lines, and authorities encourage residents to call 911 if they smell the odor that accompanies gas.The massive Parks at Arlington mall at Cooper Street and Interstate 20 shut down as the storms moved through, and management ordered shoppers and others into the basement. Employees at Cowboys Stadium were moved into the tunnels.Despite the storms, the Rangers game vs. the Mexico City Red Devils was still scheduled to go on Tuesday night at the Rangers Ballpark. Schoolchildren in multiple cities, as well as travelers at Dallas-Fort Worth International Airport and Love Field in Dallas, were ordered into "safe zones" and shelters. Golfball-sized hail was reported at DFW.DFW Airport officials told passengers to move away from glass windows and to take cover in its storm shelters at its terminals.The Federal Aviation Administration also issued a ground stop for flights coming into and out of DFW because of the storms.DFW Airport spokesman David Magana said passengers should expect delays and incoming flights may be diverted to get out of the way of the storm.American Airlines cancelled the rest of its flight schedule out of DFW for the day, a total of more than 450 flights. It said 68 planes had to be inspected for hail damage.Trinity Railway Express trains quit running during the emergency.The first tornado was spotted near Joshua about 12:44 p.m., according to the weather service, moving northeast at 25 mph.Johnson County Sheriff's Lt. Tim Jones said he was trying to find a place to set up a command center."We've had a couple of houses hit near Joshua out on 704. As far as I know we have no injuries yet."Fire officials in Joshua continued to track storms after 2 p.m., and reports were out that some areas of Burleson and Cleburne were similarly damaged from the storm.A twister touched down about two miles east of Spinks Airport in south Fort Worth as the storm system swept across Tarrant County, according to airport manager Aaron Barth. He said it caused no damage at the airport."A tornado came down for maybe 8 to 10 seconds and then lifted back up," Barth said. "It wasn't down for very long."Sirens could be heard on the west side of Fort Worth and in the Fort Worth medical district.A second tornado warning was issued for Dallas and Ellis counties after a tornado was confirmed on the ground in Ellis County near Red Oak.A tornado near Lancaster in Dallas County reportedly caused power flashes and sent huge debris balls flying into the sky.Staff writers Andrea Ahles, Jim Fuquay, Susan Schrock, Mitch Mitchell, Deanna Boyd, Patrick Walker and Steve Campbell contributed to this report.