Police respond to reports of a shooting at a Walmart in Colorado

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A Walmart in Thornton, Colorado.

Police in Colorado said there were "multiple parties down" after a shooting at a Walmart in Thornton, Colorado, on Wednesday night.

The Thornton Police Department confirmed the shooting on its Twitter account and were searching for two subjects, according to a Denver 7 reporter. The number of casualties was not immediately clear.

Witnesses say they heard multiple shots at the Walmart, and videos of the scene show an empty store with uniformed police officers nearby.

The shopping center contains several stores and restaurants, according to The Denver Post. Police warned people to stay away from the area.

This is a developing story. Check back for updates.