AN explosion at the Hoover Dam has been captured on video as thick black smoke can be seen billowing from the historic landmark.

Footage posted on social media shows a giant fireball rising at the Nevada monument on Tuesday morning.

The Boulder City Police Department confirmed to The US Sun that they have units en route to the scene following an explosion.

A tourist visiting the site captured a video showing the fire may have occurred in a building near the dam's base.

However, cops have yet to determine what part of the dam the explosion took place.