[Pfc.Green]

Seven astronauts aboard space shuttle.

Houston, Texas (CNN) -- The space shuttle Columbia, with seven astronauts aboard, broke up as it descended over central Texas Saturday toward a planned landing at Kennedy Space Center in Florida.

Search-and-rescue teams from the Dallas-Fort Worth area were alerted and area residents were urged to stay away from any possible debris from the shuttle, which may be hazardous, said NASA public affairs officer James Hartfield.

The Bush administration was preparing to convene a "domestic event" conference among all domestic and military agencies that may be involved in the next step.

An administration official said the shuttle's altitude -- over 200,000 feet -- made it "highly unlikely" that the shuttle fell victim to a terrorist act.

NASA officials said they last had contact with the shuttle about 9 a.m. EST, and it had been expected to touch down at about 9:16 a.m. EST.

Video of the shuttle tracking over Dallas showed multiple vapor trails, but NASA spokesman Kyle Herring said it was too early to determine the source.

Steve Petrovich, a police officer in Palestine, Texas, said he heard "a rumble and boom" at about 8 a.m. CDT (9 a.m. EST).

Jim Hubbs of New Boston, Texas, said he heard police discussing over a police scanner "a smoking object going southeast" that disappeared in the Bowie County area near the Arkansas state line.

Officials said no tracking data were available.

Israel's first astronaut, Ilan Ramon, was among the seven-person crew. There was no official reaction from the Israeli government, but a Defense Ministry spokeswoman said, "Like everyone else, we are feeling terrible, hoping the slightest hope that still remains at this stage will become a reality."

Columbia is the oldest of NASA's shuttle fleet, first launched in 1981. It was on its 28th mission.
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