The STS-107 crew. Seated in front are astronauts Rick Husband, commander, and Willie McCool, pilot. Standing are (from left) mission specialists Dave Brown, Laurel Clark, Kalpana Chawla, Mike Anderson (payload commander) and payload specialist Ilan Ramon, representing the Israeli Space Agency. Photo: NASA.

The space shuttle Columbia has broken up in the skies over Texas. Its crew of seven astronauts are presumed dead. Mission control lost contact with the shuttle around 9 a.m. EST (1400 GMT), about 16 minutes before its planned touchdown in Florida. Emergency procedures are in effect and search and rescue teams have been alerted in the north and east areas of Texas, where any debris might have fallen. Check the mission status center for the latest developments.

Columbia and its crew of seven, which included the first Israeli astronaut, were returning home to the Kennedy Space Center after what had been hailed as a succesful 16-day scientific research mission.

Aboard the shuttle were: Rick Husband, commander, and Willie McCool, pilot. Mission specialists Dave Brown, Laurel Clark, Kalpana Chawla, Mike Anderson (payload commander) and Israeli payload specialist Ilan Ramon.

"This is indeed a tragic day for the NASA family," NASA Administrator Sean O'Keefe told a news conference, four hours after the loss of the shuttle. President Bush was informed of the disaster and spoke to the families of the crew who were awaiting the shuttle's return in Florida.

"This day has brought terrible news and great sadness to our country," Bush said in an address to the U.S. people broadcast from the White House. "At 9:00 a.m. this morning, Mission Control in Houston lost contact with our Space Shuttle Columbia. A short time later, debris was seen falling from the skies above Texas. The Columbia is lost; there are no survivors."

An independent investigation into the loss of Columbia has been launched.

Just prior to the loss of communications the astronauts and flight controllers received a landing gear tire pressure warning. At the time Columbia was about 200,000 feet up and traveling at 12,500 miles per hour. CAPCOM Charles Hobaugh radioed the crew about the warning, a garbled response was heard from the orbiter, but contact was then lost. Hobaugh made repeated attempts to regain contact with the crew.

Meanwhile observers on the ground in Texas who were watching the shuttle streak across the sky saw mutiple objects break away from the shuttle's fiery trail. Spaceflight Now correspondent Stephen Clark was watching from Larue, Texas.

Mission control's tracking map shows the shuttle's last known position at the end of the series of red crosses. Photo: Spaceflight Now/NASA TV.

"We were outside and my Dad said "there it is!" in one piece. Then a tiny, tiny piece came off and I was somewhat perplexed. That wasn't supposed to happen. Then bigger pieces rained away from the main piece. It looked very similar to the video we saw of the Russian space station Mir reentering. Later, there was one loud boom and accompanied by smaller booms. Normally we hear two distinct sonic booms when shuttles pass over during entries."

NASA officials have warned Texas residents to stay away from any debris that might have reach the ground as residual rocket propellant could prove a serious hazard. The debris cloud from the shuttle's break-up appears to be visible in weather radar images. Reports are coming in of numerous findings of debris on the ground around Nacogdoches, Texas. One piece appears to be one of the orbiter's Orbital Maneuvering System (OMS) engine bells.

Mission control has provided no information about what might have gone wrong. Flight controllers put contingency proceedures into effect, which included ensuring all relevant data and notes were preserved.

During a mission status news conference on Friday, Entry Flight Director Leroy Cain was asked about any possible damage to the shuttle's thermal tiles during launch. The tiles are what protect the shuttle during the fiery reentry into Earth's atmosphere.

Tracking video of launch shows what appears to be a piece of foam insulation from the shuttle's external tank falling away during ascent and hitting the orbiter's left wing near its leading edge. Spaceflight Now has isolated video frames that appear to show the incident.

But Cain said engineers "took a very thorough look at the situation with the tile on the left wing and we have no concerns whatsoever. We haven't changed anything with respect to our trajectory design. It will be a nominal, standard trajectory."

At the Kennedy Space Center non-essential workers were sent home and all work on future shuttle missions was cancelled. Atlantis is in the Vehicle Assembly Building attached to its external fuel tank and solid rocket boosters. It was scheduled for a March launch to the International Space Station.