Grocery store chain Whole Foods Market fired an Oakland, California, security guard who beat and bloodied a black customer in a disagreement with store staff. The shopper was left unconscious in a pool of his own blood, witnesses said.

The incident, which occurred Thursday night, was reported on social media by Whole Foods patron Zoe Marks, a University of Edinburgh lecturer who took graphic photos of the dust-up and posted them to Facebook. "I just saw a young man violently assaulted by an armed security guard at Whole Foods -- slammed repeatedly against concrete pillars, put in a choke hold, restrained and suffocated until he was thrown face down on the pavement unconscious," she wrote.

Marks told the Oakland Tribune the customer “wasn't violent or disruptive. … There was no threat from him to any of the customers or employees.” Authorities arrived to find the man bleeding from the mouth. He was taken to the hospital and found to be in stable condition, the San Francisco Chronicle reported.

In Oakland less than four hours and I just saw a young man violently assaulted by an armed security guard at Whole Foods...

Posted by Zoe Marks on Friday, September 4, 2015

Whole Foods soon responded on Twitter, assuring Marks the company was looking into the matter. By Friday night, amid increasing protests over the store's use of armed guards, Whole Foods tweeted the security guard had been dismissed.

It remains unclear what exactly occurred between the Whole Foods staff and the customer who was beaten. A spokeswoman for Whole Foods told the San Francisco Chronicle the guard “interceded when the customer made physical contact with a team member inside the store."

The company said it is still examining the issue. "While we move swiftly to gather the facts, we want to make it clear that Whole Foods Market takes a zero-tolerance approach to violence," the spokeswoman told the Oakland Tribune.