From the Washington Post:

NASA declared an emergency after losing communication with space shuttle Columbia as the ship soared over Texas several minutes before its expected landing time Saturday morning.

The shuttle was carrying the first Israeli astronaut and six Americans, and authorities had feared it would be a terrorist target.

Fifteen minutes after the expected landing time, and with no word from the shuttle, NASA announced that search and rescue teams were being mobilized in Dallas and Fort Worth areas.

Inside Mission Control, flight controller hovered in front of their computers, staring at the screens. The wives, husbands and children of the astronauts who had been waiting at the landing strip were gathered together by NASA and taken to separate place.

Columbia was at an altitude of 200,700 feet over north-central Texas at a 9 a.m., traveling at 12,500 mph when mission control lost contact and tracking data.

NASA, while not saying the shuttle had exploded, broken up or crashed, warned that any debris found in the area should be avoided and could be hazardous. There were reports of debris seen falling.