A frantic rescue effort is underway in Minneapolis, where an interstate highway bridge has collapsed into the Mississippi River. Dozens of vehicles were thrown into the water, while some were crushed on roadways that run beneath the I-35W bridge. At least one school bus was involved, but good Samaritans and other rescuers were able to get the children off the bus and to safety. Divers have gone into the water, searching for victims as dusk begins to fall in the Minneapolis area. Six fatalities are reported in the disaster. In Washington DC, the Homeland Security Department says there is no reason to believe that terrorism might be involved in the bridge collapse. However, authorities and observers are left wondering why a bridge thats only 40 years old would give way and fall into the river. Some witnesses reported a loud rumbling sound before the bridge fell. One witness said it went into the river in just about five seconds. Three of four sections of the bridge fell either into the river or onto roads below. A fourth section is said to be unstable and in danger of collapse. The catastrophe occurred at rush hour in Minneapolis, when the bridge was jammed bumper-to-bumper with motorists. The deck of the bridge was being repaved at the time of the accident, but authorities say there was no work involved that would affect the structural integrity of the span.