Widows Creek Fossil Plant smoke stack implosion.

Watch: Explosives bring smokestack crashing to the ground

This is the moment crews employed explosives to bring a 305-metre-tall smokestack crashing to the ground at an old power plant in Alabama.

Footage shows the massive structure leaning over and hitting the ground with a thud.

Located about 105 kilometres northeast of Huntsville, the plant closed five years ago, and workers previously imploded two smaller stacks.

The federal utility is cleaning up the plant site in a $66 million project, and it's supposed to be ready for sale and redevelopment next year.