A Calgary rail bridge is collapsing, threatening to send five rail cars carrying a diesel-like substance into the Bow River.

Acting Fire Chief Ken Uzeloc says a train derailed after a section of the bridge dropped two feet (60 centimeters) Thursday morning. He says the bridge is not in the water but is slowly sinking into the river.

Uzeloc says each car could have 80,000 pounds (36,000 kilograms) of flammable product but he could not specify the liquid. He says the product is not yet leaking.

The bridge typically sits about 25 feet (7.6 meters) above water level, though water levels remain high after last week's flood.

The bridge is southeast of downtown Calgary. The mostly industrial surrounding area has been evacuated.