According to local media, citing eyewitnesses, the incident took place at about 3.30 pm local time (22:30 GMT) during the shift change.
At least two people have been shot dead and four more have been injured at a Walmart Distribution Centre in Red Bluff, California, The New York Times reported on Saturday citing a hospital official.
Those injured were in fair condition, Allison Hendrickson, a spokesperson for St. Elizabeth Community Hospital in Red Bluff said.
According to the Times, eyewitnesses heard about 50 gunshots. It is also reported that a car drove into the door of the distribution centre.
Local Red Bluff Daily News said that at least five ambulances arrived at the scene, as well as police officers and firefighters.
The Sacramento Bee reported that the shooter drove a white vehicle that wedged into the building. According to KHSL TV, a fire started at the site with there being about 200 workers inside the facility.
Dispatchers told The Sacramento Bee that the gunman was in the middle of the parking lot and that he was shot in the chest by around 03:45 p. m.
The authorities have yet to confirm the information concerning the incident.