Trace fire says the blaze was first reported at around 1 p.m. at the Medline Industries warehouse on the 5700 block of Promontory Parkway, before spreading to a FedEx building across the way.
Live updates: Massive fire breaks out at medical distribution warehouse in Tracy, evacs underway
Officials say all employees are evacuated as of 4 p.m.
South San Joaquin County Fire Chief Randall Bradley said crews are facing a challenging task because the fire suppression sprinkler system in the warehouse didn't appear to be working and the water pressure was too low at fire hydrants inside the complex.
Officers are currently on the scene at the assisting with evacuations and directing traffic.
"Promontory Parkway will be closed while fire crews work to contain the fire and ensure the area is safe. Tracy Police officers are on scene assisting with evacuations and directing traffic," TPD said in a statement.
Authorities said the fire is burning several hundred acres, a square mile each way.
Richards urges those nearby to stay inside due to the air quality. The public is asked to avoid the area and use alternate routes if possible.
Medline distributes medical supplies across the U.S. According to its website, Medline's Tracy distribution center is one of three within a 20-minute drive of each other. The warehouse is said to be 1 million square feet.
In a statement, Medline said: "Medline can confirm a fire is occurring at our Tracy, California distribution facility. All Medline employees and on-site personnel are accounted for. The safety and well-being of our employees is our top priority. We are coordinating closely with local authorities and first responders as we assess the fire's impact and will share more details as they become available."
No injuries have been reported, and no homes are threatened.
Currently, dozens of law enforcement and fire crews are at the scene, including first responders from Stockton, Mountain House, Lathrop, Manteca, the California Highway Patrol and Alameda and Contra Costa counties.
There is no indication yet about what might have started the blaze, which briefly spread to a stack of pallets at a nearby FedEx office before being contained to the Medline facility.
People are being asked to avoid the area.
Bay City News contributed to this report.
Stay with ABC7 News for the latest details on this developing story.