Reeling from a series of terrorist attacks on New York and Washington, U.S. authorities have gone on a coast-to-coast alert as they try to assess the damage from the unfolding disaster.
Aviation authorities quickly grounded all flights in the United States after the first of two apparently hijacked aircraft slammed into the twin towers of the World Trade Center in New York.
Streets in the city were closed as emergency operations teams attempted to sift through the rubble of the burning and collapsed buildings.
President Bush curtailed a visit to Florida to rush back to Washington where panicked federal workers poured into the streets, and all government buildings were ordered closed.
That action was ordered after a commercial airliner slammed into an area near the Pentagon's helicopter landing pad. Highways running past the giant office complex were closed as thick acrid smoke rose from the building.
In Los Angeles, anti-terrorist police have been put on special tactical alert. In Chicago officials ordered the Sears tower closed as a precaution. U.S. Secretary of State Colin Powell has also cut short a visit to Peru and Colombia to return to the Capital.