The U.S. space agency NASA has lost contact with the shuttle Columbia as it was returning to Earth from a mission. NASA has declared an emergency.
NASA says it lost all communication with the shuttle, as it was flying over north central Texas on its way to a landing in Cape Canaveral, Florida.
The shuttle was on its way home after a 16-day scientific research mission.
NASA has called for the mobilization of emergency fire and rescue teams in the Dallas-Forth Worth area of northern Texas, over which the shuttle was flying when last contact was made.
Videos from a Dallas television station show several white trails heading toward the ground, which could indicate that the shuttle broke into pieces.
Security was tighter than usual at the landing site, because Israeli astronaut Ilan Ramon's presence on the mission prompted U.S. space agency fears that he might be the target of a terrorist attack.
However, there is no indication that terrorism is involved.