At least nine people were killed and many others injured after an interstate bridge over the Mississippi River [Images] in the US state of Minnesota collapsed during rush hour, sending chunks of concrete and vehicles into the river below.

Reports said a freight train passing under the 40-year old bridge was cut in two on Wednesday evening. But children travelling in school bus had a lucky escape as it had just crossed the bridge when it collapsed. It clung to a slab and did not fall into the river. All children were evacuated safely.

Officials said 50 to 100 cars and other vehicles were on the two-lane bridge when accident occurred and most of them went down into the river along concrete and twisted metal pieces.

Reports said rescue workers had searched some 50 cars and the rescue operations were continuing under floodlights.

The bridge was being repaired at a time the collapse occurred and officials said it was due to be replaced in 2020.

The repair work included change of the guardrail, concrete work and replacement of joints.

Officials said at present, it seems to be case of structural failure. Some 200,000 cars use the bridge every day.